go to the start menu, and in the search box type in system restore. they will give you options of until where you want to restore your windows then just select the one you want. then click next and just wait until your windows starts again. it should be fine. it worked yesterday for me for the second time so it should work for you to.
Switch off your computer. Open the disc tray. Insert Windows 7 Operating System disc. Switch on your computer. Press any button when it says, " boot from the CD " Installation wiil begin. It may take an hour. Follow on screen instrucions. Back up data before doing this process.
You can change your window back to window 7 genuine first by typing rsop.msc in the Start or Run menu search box and then press Enter. You should then run the computer configuration process. You can as well consider using the Registry Editor to validate your windows. Visit an IT expert to fix it for you.