Computer won't post/boot

As of Sept 17th: I had just gotten done playing my ps3 and hooked my pc back up to my monitor(i use my pc monitor for the PS3 since the HDMI/Composite connections on the TV are broken.) and when I tried to turn the computer on it wouldn't post. Everything powers on properly, but the machine won't post or anything.


As of today: Ok, so I got my new motherboard(ASUS P5Q SE Plus) today, took everything out and put it back in with the new hardware, but the exact same thing happens when I turn the PC on. No post, everything powers on, no video, no response from keyboard or mouse other than they have power. Any ideas? Could it be my RAM or CPU causing this? I've tried two different video cards and end up with the same issue. Now, when I tried the second video card(An old 7800GTX) I turned the PC on, and the PSU now turns on for a moment, turns off, then turns itself back on and stays on. Could it be time for a new PSU aswell as some other components?

Current specs:

C2D E6600
2GB Patriot RAM
ATI 4850
OCZ 550w PSU

Well, the problem seems to be rooting from a bad stick of RAM. The issue with my PSU also stopped, but I would assume that a new one would be essential to the longetivity of my PC.

A good test to confirm your RAM being bad is to boot without the RAM installed. In a good system, you'll get beeping, alerting you that no RAM is installed. If you don't get an error at all, something before that in the posting sequence is screwed up.