Overheating.. could be several problems or one problem. Work through them.
The freezing is because the video card is overheating.. why its overheating however could be from several problems or just one it all depends..
First as was suggested it could very well be too small a power supply.. You could download Speed fan
http://www.almico.com/speedfan.php and if your hard dirve is S.M.A.R.T. which most new ones are then you would be able to monitor a number of temperature sensors and see where the heat is coming from. However if your PS is not putting out enough voltage or amperage then that’s a good indication of what is going wrong. From what you have posted on your system I’d say 650 watts is a min. for your system.
Secondly overheating.. from too little ram. Not enough ram will result in your processor working too hard thereby producing heat exponentially more than usual. If its Vista then 4gb is a min for serious PC’s. XP should have at least two but more than 4 is unnecessary since XP doesn’t recognize ram over 4gb’s well.
Third your Vid card’s fan may be failing or its heat sink may have become unattached or it may be simply failing. You could try it in another PC and check it or else you could try a less expensive card (which will draw less amperage) and see if the problem remains. Also if it’s a 8500 or higher make SURE you have the latest drivers installed.
Fourth cooling fans and ventilation.. fans draw lots of voltage though so it’s a trade off.. Adding fans will help but it puts you back to the first suggestion. Can your power supply handle more devices.
So there ya go..
1) Power supply inadequate
2) Not enough Ram
3) Video card failure
4) Not enough cooling…
It’s one or more of these issues. You just need to find which one it is.
As a note still another reason this may be happening is due to over clocking.. if you over clocked your processor then you need to bring it back down.. instead of over clocking try increasing your ram voltage. Your Motherboards bios may need updating and check your multiplier in your Motherboards bios and make sure you haven’t set it too high. I’m not a big fan of over clocking since its really unnecessary unless your are running multiple applications while playing a video intensive game and downloading massive amounts of porn at the same time then over clocking just makes your PC work a lot harder then it needs to
Lastly your motherboard may be failing.. but I’d wait to make sure its not one of the other reasons before getting to this one.