You should try reinstalling by Disc. If you have them already see the guide below. If not There are links in the U.S. to request such media, once you have the media proceed again following the guide. The guide mentions downloadable Retail Vista but I am unsure if they files will accept the product key. If you try these please verify with me if they work or not.
Hi folks,  I have the XPS M1530 running Vista and I really need to restore the computer to the factor image.  I follow the instructions on the dell website, hit F8 at startup, repair system options, and then the final option on the menu is "restore to factory image"  I click that, click ok, and then the checkmark to confirm the process. But once I click next, I get:  Access to \tools\dp.sc was denied.  I have no idea what to do. I ran the diagnostic programs and they all came out fine. If I log into vista, and open the recovery partition, I see that the software is sitting there (get the same error if I try to load it from windows).  What do I do?
Cannot restore to factory image, Vista XPS