Okay, so before anyone asks... I HAVE read the sticky at the top of the forum and tried everything possible to no avail.
The story so far: Several days ago I was using my PC as I do without any problems at all, it had been running smoothly as it always does (P4 3GHz, 512DDR, XP PRO, ASUS MoBo - unaware of model, 120G HD). I had just that day acquired a brand new MP3 player which had just then finished charging. It required no installation of drivers so I attached it to its AC adaptor and connected it via USB according to its manual. The instant of connecting my computer immediately lost all power, and has since not been able to start up at all. No fans moving, no HD activity, no beeps and no lights. The MP3 player I have since attempted to use in 2 other computers which it didn't ruin, so I am still unsure whether it was the cause.
The only sign of life in the PC is the motherboard light is on when the power button at the rear is on. Other than that it is stone dead.
Since then I have reset CMOS by removing the CMOS battery for several minutes. I have stripped the PC back to barebones with nothing but the GeForce FX5200 graphics card, 1 512 stick of RAM and MoBo + Processor. Same results.
I have used the power supply in another computer without problems, so it isn't that. I have also used the HD as a slave in another computer which obviously also wasn't the problem (as discovered by bare bones). I have also attempted to power on by using a screwdriver to short the power pins. No dice.
I have ensured that every cable is correctly connected, every card etc is seated properly and every neccessary switch turned on. I am at a loss as to what I can try next. I'm thinking at this point that it looks like either a CPU or MoBo problem which I'll haveto go out and replace, but would like some clarification before I do.
Any help would be greatly appreciated. Thanks.