Gah this is killing me. I have a dell inspiron 15 laptop, installed with windows vista. Every time I boot it, it run's a DSKCHK of c. Thats all fine and dandy, but from the moment the computer begins i literally have 2 minutes before it freezes. By freeze i mean the screen still shows what it had on it, but it goes all hazy and the little blue loading circle appears. Thats just enough time for me to copy files to a memory stick, but sadly, not enough time to re-install windows vista from the CD.
If you tap F8 during start up, you should access a page where you can repair the installation. If that doesn't work, you may have to 'restore to factory....' , but that would mean you would loose any data.
How old is the machine? I had to restore to factory conditions on a Dell 6400 and still had problems with Vista HP not updating (it was one of the first OS's out of the cage). I had to reinstall Vista from a disc using the sticker code, revalidate and then update everything. All was good and still is.