|You can use the Windows Vista DVD supplied with your computer to boot into the Dell recovery and restore. As long as you have not deleted or damaged the recovery partition this should allow you to use the factory drive image to restore your PC back to factory state and repair your MBR at the same time.|
Restart your computer with the Vista DVD in the drive
Press F12 during reboot and in the menu choose boot from CD/DVD ROM Drive
When the Vista DVD loads, accept the default options on each screen untill you get to the language screen, set your language then your time and currency keyboard layout, then coninue.
On the Install Now screen click Repair Your Computer.
Click NO if Windows tells you it found problems with your startup options and asks you to apply repairs.
In the System Recovery window click Windows Vista then click next to choose a recovery option.
Choose Command Prompt.
In the CMD windows type the following lines press enter after each line.
In the Dell Factory Restore window click next.
Click yes to reformat hardrive and restore system to factory condition.
If that failed to work I believe the only other option is to reinstall OS and drivers from the DVD's supplied by Dell.