Boot corrupt and unreadable, repair/re-install of Windows fails

It's my daughter's computer. A little e-Machine, 250G HD, Windows 7 32-bit on it. Out of nowhere her computer wouldn't boot up. I can get it to try to boot using the Windows disk, it gets so far, and then the repair fails saying:

The file or directory C:/Boot is corrupt and unreadable. Please run chkdsk utility.

I try to re-install. Thankfully she had backed up everything on my external just days before. It gets near the end, and then the same error comes up. I cannot get into anything else. Nothing else will load. I don't even know how I can run chkdsk. Unfortunately the computer is about three years old and she can't remember the specifics except there is only one HD in it. She had no internet at her place so it's not because she suddenly installed something. She was using it to watch movies and listen to music mostly. I'm at wits' end, can't figure it out. Any help (will have to be detailed, sorry. I know some stuff about computers, but am no expert) would be greatly appreciated. I've read through some of the other threads, but they're not exactly like what the problem is here.