Recently, few systems with VISTA had this issue: Easiest workaround is restarting software licencing service.
Start > RUN > type " services.msc" (without quotes)
Look for " software licencing service " and restart.
Now the control panel opens up fine.
After reboot, the service stops. One has to restart manually again.
Has anyone tried to boot into SAFE MODE and see what happens, Try and let me know.