Test your RAM. For beefy RAM such as you have you need a beefy test, so run memtest86 CD overnight to stress test it, or for at least 5-6 passes.
Try uninstalling your Display driver in Device Manager then restart the computer to reinstall it. Next uninstall the driver software along with it, then upon restart to VGA display driver, reinstall confirmed video driver from fresh download.
Check optional Windows Updates for more suitable display driver than Nvidia may provide. Then check your computer maker's website as they might have modified that driver.
Study the Event Viewer>Custom View>Admin to google repeat errors text and ID# to resolution. Check also the Performance log on Advanced Tools page, accessed by clicking your WEI score link at Computer>Properties. Look for cued issues at top of Tools page, Generate A System health report.
Type "solutions" in Start Search box to see solutions sent to Problems both reported and not. Win7 is interactive in this way, so always send Problem reports if asked.