Computer shutsdown...

Okay, let me get straight to the point. I recently noticed that my computer tends to shutdown after 25-40min of playing a game. This was never the problem about 5 months and the games that i play are still the same (Guild Wars, Prince of Persia 2, NHL 06). Now in a little more detail, When for example i would load up Guild Wars, 40 or so minutes into playing it my computer just turns off. I can usually just click the power button to turn it on, but sometimes i'm forced to turn the swtich at the back of my case on and then turn it back on after a minute or so to get my computer back on and running.

My specs are as follows:
Mobo: Asrock K7S41GX
CPU: AMD Sempron 2600+ 1.82ghz
Memory: 512mb RAM
Video: ATI Radeon Saphirre 9200SE 128mb
*my case is constantly open and my computer is in my basement, if it makes a difference.

Like it said, it was working fine about 5 months ago and the only hardware upgrade i had done was upgrading my 440W PSU to a 500W PSU. And it didn't seem to effect it. I first thought it might be overheating. These are the results i got from SpeedFan:
Temp01: 29C
Temp02: 42C
HD0: 29C

After seeing that my temperatures were relatively good, i paid a little more attention to when my computer turns off. I noticed that the longer i have my computer off prior to playing a game, the longer i can play the game without having the computer to turn off. Also, i noticed that the lower i set my graphic settings, the longer i can play with having the computer to turn off. I stress that i have had everything the same for more than a year now, and it was only about 5 months ago where the shutdowns started taking place. I've played Guild Wars and POP2 at med-high settings before with no problems. Any ideas? My mind is thinking that my video card is overheating or something, but it was working fine before...

PS: i posted a similar thread about a month or 2 ago, and i didn't follow up on it. It was my fault, i was away and didn't get a chance to. I hope you can help, thanks.

 

Your PSU is overheating because of a short somewhere. Make sure all the power connections are secure and fully put in and clean out any dust that may have collected in the power connector thingies.

 

Hmm let me play devils advocate for a second and ask if that is just a theory or could this actually be causing the shutdowns. I have had time to look into yet, i'll do it later tonight. When i do, any suggestions where to start, or should i just look at all the connections to my PSU and make sure everything is in the right space and in tightly..