Sounds like your bootloader is messed up.
I'd also suggest running a chkdsk after you fix the bootloader and are able to boot into Windows:
Start -> type 'cmd' (without quotes) -> right click -> run as admin -> in the console window that pops up type:
chkdsk C: /f /r
Press Enter and it will say it cannot lock the current drive and to run on next reboot. Type Y and hit Enter -> Reboot your computer and let it run through the check (it may take some time, depending on how big your HDD is).