Try loading the Command Console using the Windows Vista install CD to repair the Vista startup:
Quote:
1. Put the Windows Vista installation disc in the disc drive, and then start the computer.
2. Press a key when you are prompted.
3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type Bootrec.exe, and then press ENTER.
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More information about this here:
How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows Vista
Please let me know if this works for you.