Thank you for replying.
I am currently using Omegadrivers, yes. They are the recommended drivers for the ATI mobility chips. I don't think ATI themselves produce new drivers for these chips anymore.
However I have the 3 year old original drivers from ATI that came with the laptop. I installed these drivers when I reformated my drive, because they are on the same disk as all my other original drivers.
Sadly this did not solve the problem. Later I installed Omegadrivers again.