Here is my complete list of Vista repair alternatives ranging from checking the disk (chkdsk) to a reformat and install.

All seven alternatives have links to helpful web pages. Some you may have already tried and some may not be relevant to your problem. If you can’t boot the computer, you will need the Vista DVD or a Recovery Disk. If you can boot, the first three can additionally be run from within Vista:
1a. If you can’t boot run System Restore from a date before you started having problems. http://www.vistax64.com/tutorials/76905-system-restore-how.html?ltr=S
1b. If you can boot go to the Windows Orb (Start) > All Programs > Accessories > System Tools and right-click System Restore and choose a date before you started having problems.
2a. If you can’t boot run Chkdsk from the DVD http://www.vistax64.com/tutorials/67612-checkdisk.html
2b. If you can boot go to the Windows Orb (Start) > All Programs > Accessories and right-click Command Prompt, then ‘Run as Administrator’. Type chkdsk /f /r (note the spaces) and press Enter. It will probably run next time you boot the system.
3a. If you can’t boot run the System File Checker. This can repair many corrupted system files. It will also identify in the log file any corrupted files it could not repair http://www.vistax64.com/tutorials/66978-system-files.html
3b. If you can boot go to the Windows Orb (Start) > All Programs > Accessories and right-click Command Prompt, then ‘Run as Administrator’. Type sfc /scannow (note the space) and press Enter. This may take some time and you may have to put the Vista DVD in the drive. You can analyse the SFC log file, here http://support.microsoft.com/kb/928228/en-us
4. Copy any system files from your Vista DVD that SFC (number 3 above) identified as corrupted and could not repair http://www.vistax64.com/tutorials/86959-access-vista-install-dvd-files.html
5. Run a Vista startup repair. This can repair a lot of problems http://www.vistax64.com/tutorials/91467-startup-repair.html
6. Do a Vista upgrade repair reinstall. This gives you a new OS without changing settings, files, folders, other programs and the like http://www.vistax64.com/tutorials/88236-repair-install-vista.html
7. If all else fails, do a clean install. This will reformat your hard drive so be sure to backup your non-OS files and folders to another hard drive or other media so that you can restore them to your C drive after the clean install. Upgrade version http://www.vistax64.com/tutorials/68767-clean-install.html
Full version http://www.vistax64.com/tutorials/117366-clean-install-full-version-vista.html

RECOVERY DISK
1. If you don’t have a Vista DVD you can download/create a Recovery Disk ISO here http://neosmart.net/blog/2008/windows-vista-recovery-disc-download/ From the ISO image on your hard disk, create a CD (a DVD is not necessary as it’s only 120MB in size).

It works in the same way as the Vista DVD, i.e. boot from the disk, choose ‘Press any key to boot from CD/DVD’ and Vista will start to load the Windows files. Select your language, time/currency and keyboard then click ‘Repair’ in the bottom left corner. Within the repair option there are five choices: Startup Repair, System Restore, Backup Restore, Memory Test and Command Prompt.