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Do you get a live screen? A message saying "No Video Signal" or anything similar doesn't count as a live screen in this case. You need to get at least as far as a BIOS screen, either the system BIOS or an adapter BIOS loading.

Does the system power up? Do you hear any beeps, drives spinning up, fans, etc. If the power isn't coming on, proceed to Power Supply Failure. If the power supply diagnostics sent you back here, follow through these diagnostics as a double-check before giving up on the motherboard.
If you haven't performed the Video Failure diagnostics for a dead screen yet, do so now. Don't ignore the obvious steps, like checking the power cord and the outlet. If you skip the video diagnostics and continue with the motherboard flowchart, you could easily end up buying replacement parts for hardware that's not bad.
One of the most common failures following motherboard or RAM upgrades is improper insertion of memory modules. The levers should be lowered before inserting the memory module, and should raise themselves up and lock in place when the module is correctly seated. If you're using obsolete RIMM (Rambus Inline Memory Module) memory, the modules in a bank must be matched, and you must install CRIMMs (Continuity RIMMs) in the empty sockets. If you're using older SIMM (Single Inline Memory Modules), each bank needs a matched pair. In both cases, matched doesn't just mean capacity and speed, it also means manufacturer. I have a new page up for upgrading laptop memory with SODIMMs. For replacing regular DIMM memory, see the illustrated replacing RAM.
There are a number of reasons for a system with a good power supply to refuse to power up which were covered in the power supply diagnostics. Another reason is a failed CPU insertion, whether it's a slot or socket CPU. With good lighting, using a flashlight if necessary, make sure that any socket CPU is sitting dead flat in the socket, which means that the heatsink should be perfectly parallel to the motherboard surface; the CPU may be so totally hidden beneath some heatsinks that you can't see the edges. This problem should really only be relevant if you just upgraded your CPU or installed a new motherboard, because the CPU socket locks the CPU in firmly and the heatsink adds another level of clamping. If a socket CPU is a new install, you have to remove the heatsink and CPU to visually inspect it for damage such as crushed or bent legs. A CPU will not seat correctly if the socket locking arm wasn't raised all the way up before the CPU was inserted, or wasn't lowered all the way down after. If your CPU won't sit down in the socket properly, either the socket is faulty or you have the wrong CPU for the motherboard! I haven't seen a CPU creep out of a socket due to thermal shock for over a decade.
It's pretty tough to tell if old slot type CPUs are seated by visual inspection, so when in doubt, I reseat them. On the plus side, you can remove and reseat a slot CPU without removing the heatsink, since they form an integral unit. Make sure you correctly identify release levers on a slot CPU package, which are normally located at the top of the CPU package, to the inside of the motherboard support structure.
A stone dead CPU is another reason for a system to fail. All modern CPUs require a heatsink, and most of these are an active heatsink, with a fan on top. You may encounter a heatsink without a fan in mass-manufactured brand-name systems where the manufacturer had the engineering talent in-house to do a thorough thermal analysis and determined that the airflow over a passive finned heatsink was enough to keep the CPU within the operating temperature range. When there is a fan on the heatsink, it must be hooked up to the correct power point on the motherboard for the BIOS to monitor its condition and turn it off and on. If you just installed a new CPU and powered the system up with no heatsink, it may have failed already. If the fan on your active heatsink isn't spinning up, replace it and hope for the best. Make sure you see the new heatsink fan operating since it could be the power point on the motherboard that's failed.
If you have a system that powers up, the next question is, do you hear any beeps coming from the motherboard speaker. If your motherboard doesn't have an integrated piezoelectric speaker but does have a speaker connection next to the power and reset connections (usually the front, left-hand corner of the motherboard) attach a case speaker. If you hear an unending string of beeps, it's often bad RAM, while a repeated sequence can be RAM or video. Other beep codes have been largely abandoned since they pertained to non-user replaceable surface mount components. Beeps or no beeps, I always reseat the video adapter and the RAM, paying special attention to the locking levers on the memory sockets
Are your motherboard settings on the defaults? Whether you just put in a new motherboard or have been fooling around with overclocking, restore the default settings. This is often accomplished with a single jumper or switch setting, but sometimes it involves moving several jumpers or switches. Get the default values from the motherboard documentation. If you can't find the original manual or locate the equivalent documentation on the Internet, you may have to skip this procedure. Sometimes, the silk screens on the motherboard are sufficiently detailed to work out the defaults, but you need really good eyes to figure it out.
Although we're repeating a little of the power supply diagnostics here, stripping down the system is the next step in a "no power-up" scenario. Unplug the power cord before each change in the case. Disconnect drives, one at a time, reconnecting power and trying power up after each. Next start removing adapters, saving the video adapter for last, reconnecting power and retrying after each change to ensure you discover which component is causing the failure.
Running the motherboard without a case is a common technique used by technicians to eliminate any weird grounding and shorting issues or mechanical stresses. It also makes it much easier to swap the CPU if that's required. I normally do my bench testing on top of a cardboard box, with a static free bag or foam between the bottom of the motherboard and the cardboard. You don't walk away from a test like this or you might come back to find the box on fire! If your motherboard powers up on the bench with the same power supply that you used in the case, you have a geometry problem. Ideally, you should have a spare power supply for bench testing if you're going to do regular repair and testing work.
Make sure some standoffs aren't higher than others, putting unacceptable stress on the motherboard. Check that every standoff appears under a screw hole. The easiest way to be sure is to count the standoffs, count the screws, and make sure there are no screws leftover after you install the motherboard. There could be a short caused by a misplaced standoff, a loose screw, metal chips from shoddy materials. I've encountered standoff shorts that produce an endless string of beeps like RAM failure, without damaging the motherboard. There's also the possibility that the case geometry is so messed up (out of square or level when the cover is forced on) that it's putting an unacceptable mechanical stress on the motherboard resulting in an open circuit. If you can't find the cause of the problem, don't hesitate to try another case and power supply.
If you still have a "no power" situation with the motherboard running out of the case, there's always the last refuge of a scoundrel. Swap in a known good CPU not forgetting to install a good heatsink and to connect the fan, even just for a quick test. I try to keep around some cheap old CPUs for this purpose, just in case the motherboard is a CPU eater. It's another good reason to leave all the motherboard settings on the default "Automatic" setting, so you don't have to fool around with them at this stage. If your old CPU is bad and the heatsink fan is dead, it's a pretty sure bet that the dead fan caused the CPU failure. If the heatsink fan is working, determining whether the CPU failure was due to poor heatsink contact, improper motherboard settings, or lousy power regulation from the motherboard is a guessing game. If the motherboard is an older make and you have a couple bucks to spare, replace the CPU and the motherboard together. Replacing just the CPU, even if the motherboard tests out OK, is kind of risky and usually tough to justify from a price/performance standpoint unless the system was practically new, say less than a half a year old.
If you still have a no power situation, not to mention no beeps and no video, you're probably looking at a bad motherboard. Again, this diagnosis assumes that you went through the Video Failure diagnostics, which would have forced you through the Power Supply Failure diagnostics as well. I still wouldn't be in a hurry to take a gun to the motherboard. Get your system operating with a replacement motherboard and all the identical parts that the old motherboard failed with before you make the trash can decision. I just added some illustrated instructions for replacing a motherboard to this site, including installing a new motherboard.

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R.I.P My Brother, J.M.S
USAF 1Lt, Computer/Network Tech
Air Force Security Forces
Comp Specs
CPU: Intel Core i7-965 Extreme Edition 3.9GHz
motherboard: Intel X58
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