Dimension 4600C motherboard

I have a Dimension 4600C and because I am not at it right now I don't know too many of the other specs. But the problem is that when I would turn it on it seemed to be sending nothing to the monitor. Dell told me it was the video card, but when I tried my card in a different system it worked fine. They then told me it was the motherboard. Today I ordered a new one from them, and then started seeing things online saying that it's the 4600C's power supply that dies. My question is, are the symptoms of a dead power supply similar to a dead motherboard, or if the power supply went would the computer do nothing when you pressed the power button? Because I know that it seemed to start up, and it seems to me that if the computer does anything at all then the power supply is intact, but I don't really know a whole lot so...

 

Without the ps the computer is a useless piece of metal and plastic so if the ps is failed the comp would do nothind at powerup no lights no noise no magic.

 

Okay, I guess that would make sense logically. So it better be the motherboard then.

Thanks