I just built a new computer for a client of mine. The computer consists of:
M3N78 PRO AM2+ ASUS
AMD 64 X2 7750
4GB Corsair DDR2
6800 GT 512
I've spoken to a few friends about it and they think the PSU is fine, however, the only thing that turns on in the entire tower is the motherboard. None of the fans wind up (including the PSU fan), as does nothing else. I am completely stumped. This computer is quite similar to mine with the exception I have a quad core and 100W more than she does. I just can't figure it out. Any help would be appreciated.
A case speaker is very helpful when diagnosing hardware problems because the motherboard will give you error beep codes and tell you what is going on sometimes. You should look into buying one.
From the description you gave, there could be a motherboard, memory, CPU, or PSU problem, or you might have something causing a short. Go through that checklist and make sure you have everything checked off.