Troubleshooting suggestions

[Ghryphen]

For a little while Stang had to restart the computer 4 or 5 times before it would start up, it would just stay blank with no POST. Now it will not POST and just stays blank no matter what we do.

I took out all the non-essentials with no luck, I then disassembled the whole thing and then put it back together again without luck still. I purchased a PSU tester, and it indicates that the power supply is OK. I am down to thinking that it is the motherboard or CPU.

I am wondering which is more likely the culprit, and if there are any tests I could do to try and figure out which one.