Back in the bad old days when a program locked up, you could reboot (control-alt-delete) or cycle power to regain control. Windows NT, ancestor of today's windows fixed that. Control-alt-delete brought up Task Manager which allowed you to select the errant program with the mouse and shut it down.
Windows 7 seems to have broken this handy feature. Task Manager still come up, but the mouse doesn't work, which makes it nearly impossible to do anything useful with Task Manager.
"Nearly" means there are some keyboard short cuts that allow the user to do mouse things with keystrokes but few people remember what those short cuts are. I surely don't.