Backups are always handy.
You tried booting from the Windows 7 DVD and that too isn't helping?
F8 Safe Mode can sometimes work and get you through.
If checkpoints were being made, which is automatic default, you might but some driver updates and others can be trouble.
If you can run chkdsk that is also sometimes able.
If you are low on disk space...?
Paragon Software CampTuneX $19 can redistribute space and check and see if it does more, like make an image.
WinClone 4.x $29 is Mac utility to make a disk image of Windows (be sure to have non-system drive to use to store it on) and while slow and can fail on restore sometimes does have its uses.
But try with Windows DVD -- and be prepared to reinstall. Windows 8 has improved the ability to refresh the OS and leave files intact, and added a better File History that is automatic once setup to make backups (but not a system image) and works similarly to TimeMachine in some respect.