Press Control Shift and Escape together to bring up the Task Manager. Click the Processes tab and from the File menu, select New Task and type explorer.exe into the box then hit Enter.
That should bring things back to normal but you probably have a malware infection so download MalwareBytes from http://www.malwarebytes.com, install and update then restart the computer into Safe Mode with Networking by tapping Function 8 before Windows loads.
Run MalwareBytes Full Scan and when it completes, click Show Results and then Remove Selected. Restart back into Normal Mode and see if that helped.