Research the drivers
situation for your graphics card. Try all Windows 7 drivers including beta, especially WHQL. Did WIndows Updates deliver optional drivers?
Reseat your graphics card, test your RAM, swap your RAM modules, then test your HD using maker's full diag/repair CD scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.URL
This clears your hardware, but still check all connections and cables, swap cables.
Check for repeat errors in in Event Viewer>Admin view and Diagnostics>Performance logs, the latter by clicking thru your WEI score at Computer>Properties, then Advanced Tools. Look for issues cued on that page, and Generate A System Health Report. Type "Problem solutions" in Start Search box to see if any have been returned - always
send error reports to MS for this reason.
Many have had success swapping graphics cards even with a borrowed card as this tells you for sure if that is the problem. DId you run the Windows 7 Upgrade advisor to check for hardware compat?\
You can also try installing 32 bit which is included in your license as an either/or choice. 4gb is right on the border for 32/64, and 64 bit has driver
problems frequently. It won't hurt to try the difference for yourself - it kept me from going back to 64 bit.