New Computer Graphics Problems Please Help!

Hi everyone, I just bought myself a new computer to replace my very old but reliable gateway 835gm.. the video card and power supply final went in that so i did alot of research and ended up going with an HP pavilion computer then upgraded the video card and power supply...

the system:

motherboard: not sure
cpu: intel i7 2600 3.4ghz
gpu: nvidia geforce gtx 660
psu: thermaltake 600w
ram: 2 4gb sticks
1 dvdrw drive, 3 fans
windows 7 64 bit home premium

The problem i am having with it only happens when i run a newer video game or a autocad type of program.. The game will start but at a time the screen with flicker to all different colors, and sometimes it will freeze and need to be rebooted and others after several seconds it will recover then i will get a message "display driver has stopped responding but has recovered". The computer wants me to update my nvidia driver to the newest release, so i try to do that. but half way through the install of the driver the computer will shut down randomly.. on reboot the computer will not reboot normally after the windows loading logo the computer keeps glitching and it ends up going to start up repair and restoring itself to where it was before the update. I have been trying to find an answer to my problem all over online , but cant seem to do anything that has worked as of yet. Ive been trying for several days and the whole situation is really wearing on me. Can anyone please help me figure out what my problem is? Could my video card be defective? Any help is greatly appreciated!!