Have recently reinstalled LR and updated to 4.1
Several times but not always, after I exit the software (close window red X) and later try to start it from a shortcut, nothing happens. Investigating in task manager I found that the lightroom process was still running. Forcing it to stop then allowed LR to start normally.
Win 7-64 SP1 fully uptodate, hi-spec PC.
Europe, Middle East and Africa