Recently I've been having this problem with my PC in that it just all of a sudden turns off (mostly in the middle of games - Warcraft3 in particular) it doesnt restart simply turns off and stays off. I then turn it back on again and nothing happens, I might get a flash of power in the green light but it wont turn back on.

When I unplug the power lead and tap my computer a few times then plug it back in it usually turns back on again fairly soon.

I'm wondering what the problem could be, I'm pretty sure its not software related as everyhthing is up-to-date ie. drivers etc

Is it the power supply? overheating? graphics card - since it only seems to be in games? faulty RAM installation? I have no idea... this is all ideas i've got from oter messages.. but its weird it doesnt turn on again which leads me to think something about the power supply.

Some other info:

Pentium 3 800
394MB PC133 SDRAM
NeVidia Geforce 2 MX graphics card
Soundblaster live sound card
Windows XP Home

Any advice would be great.

It can be power supply. change powr s. if
you can. Or if you have a lot of FANS or
stuff that need a lot of current so the
power supply turns off, maybe i am not
sure.
get a better power supply that has about
350 W

Yeah.
I doesn't sound like a RAM problem. If you were hitting a bad section of memory it would normally lock up or reboot or something.
Not just power off.

And if RAM wasn't installed properly, it wouldn't boot. It would give you a memory beep code on bootup.
But it doesn't hurt to reseat it if you think it might be loose. But I don't think it will resolve that issue.