is my motherboard fried? (daewoo C8641x)

Just installed a new PSU to my ageing PC, booted up fine into W2k. Suddenly there was no display on the screen - of course I couldn't see anything to crtl/alt/delete so I hit the power button for the usual 10 seconds but the machine wouldn't switch off, so hit the reset button and it switched off but is now totally dead. Nothing happens when I press the power switch. Tried another switch, same problem. I can get power to the processor & fan by connecting the switch to the "factory use only" part of the motherboard (sorry, i don't know the technical names for these components but a friend managed to find some kind of diagram...I assume it's where they plug in the power switch to test that the motherboard powers on on the production line?) and holding the switch in but it won't get as far as a boot (and as soon as I take my thumb off the switch, it dies again), the processor will start and the fan goes around but that is it.

There is no beep code, it doesn't get that far. It's completely dead until I plug the switch into the other connector on the motherboard. Which I assume means I'm getting power to the motherboard, somehow...

The PSU is fine. Tried another PSU which I know to be fine, same problem. Have tried reseating absolutely everything in the machine to no avail. Taken the CMOS battery out and replaced it with one from a working machine also to no avail.

Anyone got any ideas? Have I fried my motherboard/processor? It was working perfectly then suddenly just died...

I'm sorry I don't know the names of the various parts of the motherboard...The motherboard is a Daewoo c8641x if that helps - I can't find any information at all and I don't know where to start!

Many thanks

OK, a little more coherant now I've read back through the board a bit. If I plug the "reset" cable into the "power" connector and hold the reset button in, the CPU fan will start to go around. But with the power cable plugged into the power connector, nothing. That's what I was trying to say, very ineloquently!