Please restart the computer and immediately begin tapping the F8 key to enable the Advanced start menu.
If 'Repair your computer' is an option, please select it.
If the option is not there, you will need to boot from the Vista dvd, then select the Repair your computer option at the Install Windows screen as shown below.

Once you get to the System Recovery Options screen, let me know what drive letter is shown for the operating system, as illustrated below.
