Win7 task manager can not adjust how it is going to

First press Ctrl+Shift+Esc key combination to see if the task manager can be called up, if not, first check if the system group policy settings have problems: in the group policy editor In the middle, find “user configuration →management template → system → CTRL+ALT+DELE option”, find "delete task manager" on the left side, directly change it to "not configured". If it still doesn't work, there may be a problem with the system file Taskmgr.exe. You can search for the file from other operating systems of the same version (by default under C:WindowsSystem32) and copy it to the same name folder of your system.