This is what I would do. Reinstalling Windows Instructions, without losing files!!!
1. Get access to another computer
2. Get a blank 4GB or more USB
3.Install Unetbootin on the computer
4. Once installed look for Select Distribution choose Parted Magic [Latest]
5.Use Unetbootin to burn the iso on the USB
6. Once completed boot from in you computer that is not working.
7. Once in the Operation System open Gparted
8. Use Gparted to the resize the Partition that is your computer C: Drive (look it up on youtube if you don't get this part)
9. Partition the Unallocted Space to NTFS format.
10. Exit the OS
11. And Reinstall windows on the new partition
Sound difficult but its not lol.