Have you tried a repair with your Windows disc? Go to BIOS, choose your DVD as Boot, insert the disc, and choose Repair computer. It may be you have no disc, but Windows is in your drive as a separate, hidden partition. I'm not good with the latter, someone else has to comment that.
This may be one of the everlasting problems - quite often it's faster to reinstall Windows, instead of fighting with some remedy. People have fought for weeks to solve it, yet they couldn't...
In any case, in future, have your hard drive partitioned, and your personal files in another partition than Windows, that way you can freely format the C, with no need to worry about your own files. Or better still, have your personals on another drive.
Best of luck...