Try these steps, hope they will help you:
1. Copy all your files and documents to an external storage device.
2. Shut down the computer.
3. Turn the PC back on and hit the F8 key repeatedly until the Advanced Boot Option Screen appears.
4. Click "Repair Your Computer" if you are not already on it and then press ENTER
5. choose your country and click OK
6. On the "System Recovery Options Screen" click "Restore Application" which is the last option.
7. Follow the on-screen instructions
8. When prompted, click on "Full Factory Recovery"
10. Click "Yes"
11. you will notice for a while it seems like nothing is happening, give it some time.
12. After some minutes, recovery will complete and you click "Finish"
Let me know if it helps you,