Open the Start Menu.
In the white line (Start Search) area, type regedit and press Enter.
If prompted, click on the Continue button in the UAC prompt.
In regedit, go to:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies.
If you see ActiveDesktop under Policies on the left, click it and delete everything that appears in the right-hand box except Default.
If you see System under Policies on the left, click it and delete everything that appears in the right-hand box except Default.
Reboot.