Hi gregor77, relax your computer is not broken.
1) right clic comodo tray icon, point to Sanbox Security Level, clic on desabled. The sandbos is now unactive.
2) go to Defense+ > Unrecogniezd Files. Normally your disinstaller should be there. If yes, clic on it, then on the meve to button, then Trusted Files.
3) push on the 3 following keys simultanously ctrl, alt, delete. It'll open the Windows task manager. Clic on the above left tab (tasks not the processes), select all the tasks mentionned in the window and clic on the below left tab (end of task). Hopefully, it'll unlock your computer.
Well, if your computer won't unlock, the do a manuel reboot. As the uninstaller has been simply sandboxed it shouldn't be corrupted. So relaunch it.
Tell us if everything is back to normal.