Go to Start>Programs>Accessories>CMD to open a command prompt. Type regedit to load registry.
Go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Check the settings listed below:
Double-click NoRun on the right pane and change it to from 0 to 1.
To restore the Run command, reverse the steps by changing 1 to 0.
As this states if you see the number 1 change it to 0.
Hope this helps. Good Luck!