Weird things happening to my computer in steam

[DrunkPanda]

I just got a new computer and I was testing it out with counter strike source. Anyway, for some reason, when i set the settings to max, I get the same slowdowns and stutters and shit as when I set it to medium with no AA or AF. This makes no sense to me. So I did the netgraph thing to track my fps when I had max graphics settings enabled, my fps would jump all over the place from 100+ fps one second to 20 the next seemingly randomly (this happens when there is nothing really going on in the match, no explosions and stuff). Why does my fps jump so drastically and how come my game STILL lags when I set the settings way lower?

Another problem I had was that during matches, my computer has randomly shut down a few times when I'm playing. It is very weird because it is not a normal shutdown, my monitor completely turns off and acts like it has been shut off but my pc acts like it is still on (light stays on and I can hear the fans working), which forces me to hardboot the computer. Anyone know what could possibly cause this to happen?

I have a windows vista 64 bit operating system if that helps.

p.s. I posted this message already, but I accidentally posted it as a reply to someone's thread in the steam forum instead of as a new thread.

 

[-Psy-]

Sound like it's related to your power supply. Post your system specs please.

 

[DrunkPanda]

intel quad core 2.4 ghz processor
1 gb ram
500 watt powersupply
256 mb geforce 8600 gts graphics card