Hold down the ctrl and alt keys and press delete.
Select Task Manager.
In the bottom left select More Details ( if it's not already selected ).
Click in the Name column header to arrange the processes in alphabetical order.
Find the process Windows Explorer, then right click on it and select Restart.
When the process has restarted, close Task Manager, then right click the Start Menu icon, select Command Prompt (Admin) and click ‘Yes’ to the uac prompt.
Enter the following command and hit enter ( Note that there is a space between slmgr and -rearm )
slmgr -rearm
Restart