I would check ram timeings first, if they are right would assume its a problem with drivers or bios, you said you reinstalled the operating system if youve got disc and its retail version reinstall the 32bit os see if that does the same thing (wont need a key to test it) or see if you can borrow another disc doesnt matter what the os is its just to test it, if it turns out it is the 64bit thats the problem check things like sound card and other cards have the proper 64bit drivers, if its not that look on evga website see if theres a known problem with your bios version.
try looking at event logs see if they provide any clues.
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