STRANGE PC MAINBOARD PROBLEM.

All of a sudden my PC has been really doing something strange.

It will hardly start up in the normal way.

I turn on the PC and All that happens is that the Fans/HDD power up, and
then I get one Flash of the lights on the K/B and then nothing. Just sits
there with the fans going.

I have removed all components and power cycled the beast, and have got it
down to possibly the mainboard.

I reflashed the Bios, but still the same problem.

Reset CMOS.

Now here is the STRANGE part. If I manage to get it to boot, It will boot
every time after that PROVIDED I don't leave it off for more than a couple
of hours.

Then the same problem.

Even stranger, While the power was on, but PC had failed to boot, I turned
off the power at the socket, turned it back on, and then tried.

Started up first time.

Any Ideas?

If not Is there a N.G that may help.

Thanks

Mikey