My sister asked me to look at her Dell Inspiron 1521 that will not power up at all. The battery was replaced and nothing. I checked the voltage from the transformer, it was/is reading 20v dc. I reseated both sticks of memory and the hard drive. It doesn't matter whether you use battery or wall power; nothing, no lights, no beeps, nothing appears to be running i.e. fans, hard drive doesn't spin up. I detect absolutely no life what so ever. I'm thinking motherboard but wanted to get other opinions first.

Thanks for any and all advice.

Could be a broken connection on power jack socket, tend to break away from the board

could be what popeye said.
i had a laptop that came to me for repairs with the same thing, i removed the CPU, and battery, waited like 5 minutes, which completely resets the dell inspirons, then reconnect everything, should start up, just reinstall the BIOS and OS. should be good. if not motherboard went south on you.