What overheated?

I was playing a fairly hardware-intensive 3d game when all of a sudden the computer shut off. I noticed that there was a faint smell like burning plastic coming from the computer, and the PSU was very hot to the touch. This had happened to me once before while playing the same game. This time, however, my computer won't turn back on. When I hit the Power button, all lights flash for a split second, the cpu fan does about a half-rotation, and then nothing happens.

I have decent familiarity with computers, and built the one I'm talking about. I'm afraid something must have cooked to death but I don't know what. Does anyone know what component it's most likely to be? i was running the CPU at default clock, and my video card was slightly overclocked. The LAN connection light is still on, so there's power flowing through the PSU to the motherboard. Please donate any suggestions you have!

I would start with a different psu. (they can partially die)

Yep, that was it. Had a friend swap in his PSU and it booted up fine. Ordering another one now.

Thanks!