In Vista, the procedure to fix the master boot record is a bit different. You have to start up Vista in the Recovery Environment and then run the bootrec command. Here’s how.
First, load up the Windows Vista disc in your drive and press any key to boot from the disc.
Choose the language, time, currency, etc and click Next. Now click on Repair Your Computer.
3- Choose the operating system to repair and click Next. When the System Recovery Options dialog comes up, choose the Command Prompt.
4- Now type bootrec.exe and press Enter. This will rebuild the boot configuration data and hopefully fix your problem. You can also run the command with switches to fix just the master boot record (/fixmbr), the boot sector (/fixboot), or rebuild the entire BCD (/rebuildbcd).