260GTX Shutting down my computer?

I have a GTX 260 and sometimes when I play games on it my computer just clicks off. I have tried reinstalling drivers, and upping the fan speed. Why would it be doing that and how can I fix it?

Here is some info on my computer to help:
-I just reinstalled Windows Vista and I have the newest driver but I don't think I have the newest BIOS.
- That is my power supply. http://www.newegg.com/Product/Product.aspx?Item=N82E16817159055
- I have a Q6600, with 4 gigs of Patriot DDR 800 ram, and a MSI P35 Neo2-FR LGA 775
- I also have a Lian Li case (if it is overheating maybe this will help) http://www.newegg.com/Product/Product.aspx?Item=N82E16811112130

I looked for a troubleshooting forum but I didn't see one so I'm sorry if this is in the wrong forum.