I changed my graphics card from geforce 260gtx to a asus geforce 590 gtx.  my computer works when I surf the web but when I got to play games after a few minutes the computer shuts down and restarts.  Anyone have a clue what the problem might be?

Sounds like a heat issue.  Make sure your fans are clean and working.  Not only your GPU fan but all your fans.  You could download GPU Temp and see what your temps are at reboot.

could also be the power supply. check the specs on the new card and see if your power supply is big enough.

Yep. I'm with Goober. Had the same problem when upgrading to a bigger GPU.
Turned out to be the PSU. Check the event manager/log.
Hope you get it fixed.

if this didn't start happening until you replaced your card I would be suspicious that the old cards drivers were not  completly removed before you installed new drivers for the new card.

go into safe mode

uninstall your nvidia software and go to device manager and remove the display adaptor then reboot and reinstall

Minimum System Power Requirement (W)5 700W what size psu do you have?