Hi vittau,
I'm not sure if my post will help you but I had a simialr problem with windows activation and a new graphics card, MS didnt offer any real solutions to the problem but I poked about a little and found I had installed a windows update > KB971033 < This was messing with the driver for the graphics card AND a drive for a antivirus program, it only messed up once either where installed after the update.
This update is regarding windows activation.
If you go to control panel, programs and features.
On the left hand pane, click VIEW INSTALLED UPDATES
Search down the list, if you find KB971033 you can remove it, reboot and see if that solves the problem.
Hope this helps you,
Mart.