ok i cracked open the case. power supply and this is what i found
+3.3V @22A
+5V@25A
+12V1@18A
+12V2@18A
-12V@0.5A
+5VSB@2.5A

i think it might actually only be a 400Watt PSU as inside it says all combines shall not exceed 401.5W

Well, it has two 12v rails, but definetly not a 500W PSU. Your numbers are close to my Antec380. Nividia claims a 150W draw for the GTS250 and requires a minimum 450W supply (specifications tab here :http://www.nvidia.com/object/product_geforce_gts_250_us.html).  However, your 12V rails do provide 18A, and that is *just* enough to supply the 150W needed.  I assume the video card has a separate power connector? Ie it's plugged into the motherboard of course, but also has a power cable attached to it? How many HDD's and Optical drives do you have? (they also require 12Vpower).

The over heating is definetly a possibilty, either CPU or GPU. That usually takes a few minutes though -you play for 3-10 minutes then boom, reboots, and the BSOD blames a low level sywtem driver, like a motherobaord driver.  If it's a power thing, it will crash when the screen is really busy and blame the video card driver.

So we are back to the 'whose to blame?'.  Follow these instructions to turn off theauto reboot, so we can see whose faul the crash is: http://www.tunexp.com/tips/maintain_your_computer/disabling_blue_screen_of_death_auto-reboot/

If the error message has anything to do with Nvidia, you are going to need a beefier power supply. A good PSU will outlast several systems, so it is a good investment.

i have 2 hard drives in it, one i put in myself when i got the computer, and one dvd/cd optical drive. sometimes it doesnt blue screen, but just freezes forever until i restart it, is there any way i can get some data out of a freeze like that?

It looks like each one of those +12V rails can handle a little over 200W power. That means that your PSU is ill-suited for even a mid-range video card. Your PC is probably locking because you're stressing the video card too much while giving it too little power to work with. I'm guessing that your PSU is a generic or otherwise less-than-reputable brand, too, which makes it even worse.

My advice: Replace that PSU with a Corsair 550VX. It has one single +12V rail that can handle almost 500W of power, which should be more than enough for your needs, and Corsair has a history of being an extremely reliable hardware manufacturer.

And while you're at it, you might want to look at replacing your video card too, but there's so many things wrong with your build that I wouldn't have pulled the trigger on it in the first place (Why a Core i7-920? Why are you using a 32-bit OS with a LGA1366 mobo/CPU?)

go to advanced system settings by right clicking computer, start up and recovery button and uncheck 'automatically restart'.

Then you should be able to see the blue screen error message.

dad bought me the pc. It came with vista 64 but dad is very stubborn saying 64 bit OS were shit and he refused to let me keep it, so he unistalled vista and put 32 bit xp on. Eh nothing wrong with an i7 is there, its bottlenecked yes, but I didnt have to buy it :P. I have a collermaster power supply, which im assuming comes with the centurion case, ill look into getting that new power supply, in the mean time i took out the other hard drive to conserve more power for games. Also, I think I might either get a 5770 or 5870, any thoughts on this.

There's nothing wrong with the i7-920. It's just way, way overkill for gaming, since games don't make use of hyperthreading yet. But if you got it for free, then more power to you.

Cooler Master make some excellent cases, but their PSUs are on the lower end of the quality spectrum. That would definitely explain it.

For gaming, I'd recommend the 5770. The 5870 (and 5970) are basically "uber 133t e-penis" cards that offer substantially more performance than you'll need at this point in time at the cost of boat-loads of cash. If you're running 1920x1080 or lower resolution, the 5770 will allow you to max out most games.

okay thanks guys U have been a lot of help. Im getting windows 7 as soon as my careers teacherr files my University enrolment and I get my 50$ business edition discount, at the same time Ill get the psu and 5770. Again you have all been a great help. Ill post here again when i have the new gear to tell you all the results