If you compressed your hard drive (the compression feature that comes with Windows) and then your system cannot boot, follow these tips to try and fix it:
http://www.thewindowsclub.com/windows-will-not-boot-compressed-system-drive
I don't see this on the article but i could add this,
Backup you system regularly, make a system image
So if none of the tips help then you can do a system image restore.