This would not be a setting issue..... this is driver or corrupted OS issue.
I don't want to disappoint you or anyone. But at this point it is past time to really be troubleshooting any issues with RC's of win7
wait till the RTM hit's shelves and install that. Your problems my have already been resolved.
Only other thing you can do is install all the latest drivers for your PC and hope that resolves the issue.