I was able to fix the resolution problem. In my case it was the use of the nvidia lightboost hack. Apparently the created custom resolutions I used when testing it a year ago caused the trouble. After removing it completely I was able to set resolutions ingame (list was blank before).
http://www.blurbusters.com/zero-motion-blur/lightboost/I used the ToastyX app for testing as well as removal. Maybe it helps someone.
