built-in iSight not detected in main account but ok in another one

Hello,

After I have updated my macbook pro to MAc OS X Lion from MAC OS X 10.6.8, the webcam worked ok for one day, and then for unknown reason, I couldn't use it any more.

The error occue with both two apple apps I have tested, Photobooth and facetime. It just give an error message telliing that the webcam is not connected.

I have tried to remove preferences folder from ~/Library to get it rebuilt but no joy

If someone can help ...