Unless others can help us, I recommend Reinstall windows, you can use an external hard disk, a normal spare Hard Drive (formatted), a large flash drive, CDs, DVD's or my favorite Blu-Ray Disks to backup. or I forgot try to repair the windows installation which keeps programs and settings and other files but fixes the windows files if their is any missing or damaged.
Edit: My opitnion get an external hard disk, they are very cheap and you will always use it, even keep all your music, Videos and Photos ect. on it.