I recently ran into an issue with my computer. After I moved my PC downstairs, I've had intermittent issues with my computer freezing at the BIOS Splash screen (before any sort of initialization or POST). A quick reset fixed it generally, though twice it messed up my BIOS (which I fixed moving the jumper on the board). Anyways, I just got done tinkering with Ubuntu and I restarted my computer. This time, nothing popped up. No picture is coming up, and my keyboard and mouse are not receiving power. However, all the fans (CPU & Case) are working. I listened in to see if the HDD was accessing and it definitely didn't sound like it was, so I don't think it's my video cards. There aren't any beeps or other out of the ordinary noises (though the fans dial down a bit after being on for 10 seconds or so). However, there are two different lights that stay on constantly on the motherboard, one green and one purple. Also, both video cards have two red lights that stay on. These lights are normal, but they don't stay on constantly after boot up.
I built this PC back in Aug. 08'. It has a Corsair-TX 750 power supply and 4GB DDR2800 Dominator (Corsair as well maybe) RAM.