Any problems with that GPU? Keep it to yourself then. A 9800 GTX is still widely used in gaming PCs.
Try rolling back your drivers and then updating them again.
Now you just need to explain how that is magically supposed to change something. Hoping that some usually unwanted driver leftovers solve the problem? "Downdating" or updating a driver can solve problems. But surely not installing an older driver just to replace it with the "old" new one a minute later.
Doesn't matter anyway.
The behavior monitoring of Microsoft Security Essentials was the cause. Thought I turned that off months ago. Now it seems to work.