Computer crashes after playing games at high resolution

Hey everybody!
I'm new here so I don't know if there is any other topic related to my problem.
So, as the title says, when I play games at 640 x 480 (specifically "Need for Speed: Most Wanted") it works great without any problems. Also, with Minecraft, it opens in a little window and, when I play, while it's at that size, it works fine.
BUT... when I change the video settings of "NFS: MW" from 640 x 840 to 1600 x 1200 (that's my monitors' * resolution) or when i play Minecraft and make the window a bit bigger and play for a little while, my computer crashes :(
Specifically: the sound "lags" while the screen is black and my computer makes the same sound as if it boots up. And what I have to do is switch it off from the main switch and just boot it up with a screen saying "Windows didn't shut down properly..." bla bla... and with the options of going into safe mode or just run windows normally.
- My graphics card is a NVIDIA GeForce 9600 GT with "Approximate Total Memory" of 1777 MB. My current display is 1600 x 1200 (32 bit) (60Hz)
- Operating system is Windows Vista Home Premium
- Processor is Intel Core 2 Quad CPU Q9400 2.66GHz
- RAM is 3070MB
(For all the info I just looked at "dxdiag")
Thank you for your patince to read all this
- Alex

*I have dual monitors

P.S. I'm not a hardware guy. I'm more of a software guy so please explain in a bit more detail so that I can understand
 
Have you thought about upgrading to Windows 7? I think your hardware would support Windows 7, 64-bit. I use the same video card (see my specs). What is the make and wattage rating of your power supply? Have you gone to the Nvidia support website and downloaded and installed the latest video driver for your video card and operating system?
 
Have you thought about upgrading to Windows 7? I think your hardware would support Windows 7, 64-bit. I use the same video card (see my specs). What is the make and wattage rating of your power supply? Have you gone to the Nvidia support website and downloaded and installed the latest video driver for your video card and operating system?

Firstly, I have upgraded my graphics card and I don't want to change operating system.
Secondly, I kinda searched the forums and it seems that most people who have similar problems changed their power supply and they were OK. The make of my PSU I don't really know but my wattage rate is 405W. IDK is that low? If it is, then I'll change the power supply and maybe you could
recommend what wattage rate should I buy according to my system specs.
Thanks for replying
 
Yes I think you should go for a good brand 650 Watt. Brands like Corsair, Antec or Thermaltake
 
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