Re: Windows cannot start
Windows sounds hosed.
If you made any recent changes that you think might contribute to this problem, you might want to use the Recovery Console to try and change it back.
You could do a repair installation. This will basically repair windows, but keep the rest of the computer the way it is. You *should* have no data loss, aside from operating system files. This is likely your best choice.
Your other option would be to use a Linux Live CD to boot into a temporary linux operating system and backup the files from there. Then simply reformat and reinstall.