Monitor turns off, system hangs

This problem occured for the first time when playing Medieval 2 Total war. I started the game and few seconds after loading monitor turned off, I could hear some sound glitch repeating. I couldn't do anything, tried to press restart, nothing happened. Had to shut down and turn on the computer. Since then I can't play any games, that same thing happens... Monitor turns off and sound glitch repeats. In M2 Total war case it happens even when I'm in main menu, in other games it happens very shortly after loading. What I tried: reinstalling my sound card's C-Media drivers, updating my video card drivers, it didn't help. Thought this happens because my video and sound cards share the same IRQ, I moved sound card to other PCI slot, the IRQ changed and it actually helped for awhile, I could play games without a single problem for about a day. The next day I turned on the game and BAH the same thing few second after loading... My PC specs:

P4 2.8 HT
6600GT
512 mb ram
win xp

Please, anyone, help I can't play anything and have no idea what's wrong...

 

I think the fact that the problem disappears and reappears out of the blue shows some faulty or broken hardware. Thy taking out parts, cleaning the dust off them and replacing them.
The RAM could be a bottleneck. What brand and age is it?

 

RAM brand is VData. Age somewhere around 1.5 year.

This problem is just ridiculous! Few weeks ago I moved RAM to other slot and it helped. I could play games with no crashes for few weeks until today... When playing today, monitor turned off and system hanged... And now it happens everytime I start the game again...... What's wrong????!! This is driving me crazy..

By the way, then this happens, I can't restart computer, I have to shut it down. But before shutting down if I try to press restart, then after shutting down it shows that my processor is only 1.90mhz (it's 2.80 HT). I have to restart next time I turn on the computer in order to have 2.80. But it doesn't happen if I don't try pressing restart then this crash occurs.

 

Anyone?

 

Hia,
Try downloading one of the free Processor checkers/Diagnostics what you want is a burn in like test with MMX SSE SSE2 etc, i was having the same kind of problems and tried everthing before discovering it was the processor Failing MMX.