Two more ideas:
Do You have previous system restore points?
You can check it in the "help and Support Center"->"Undo changes to your computer with System Restore "-> restore my computer to an earlyer time. If You select the last restore point, then it may restore a correct system, which will work perfectly.
If not any restore point is exist, or all of them is too old (after it, You've installed programs, and so on), then try to use the "sfc" from the start menu->run like this: sfc /scannow , which will check Your system files against to the original installation files, and it restores the correct ones. Therefore it does not harm Your files, just the system, but IMHO please notice, to use the System restore is a little bit risky operation, so I suggest to do it with extraim care.