iTunes doesn't open any more

My iTunes doesn't open any more all of a sudden, though Task Manager has listed it in "Processes". Quicktime and everything else works, though.
I've tried de-installing and re-installing serveral times.. Even older Versions (iTunes 10.5) won't work.
Can you tell me what to do?
Fyi: I'm using Windows 7 and iTunes version 10.7.

Thank you!