Hi Jesper
Do you mean you deleted the Common Files folder from inside either the Program Files or Program Files (x86)
If so, Windows should not have allowed you to do that, it is an important folder . . .
Is that deleted folder in your Recycle Bin, if so, right click and choose Restore, to put that folder back
Windows will continue to function without that folder, however, some 3rd party applications you have installed on your PC may not after deleting that folder . . .