The PC Restore feature on Dell delivered Windows XP computers depends on a custom Master Boot Record for proper operation.  If you have ever reinstalled Windows XP without making use of the PC Restore feature, the special MBR gets replaced by a standard MBR which does not contain the information about the PC Restore image.  It is also possible to re-write the MBR, as some have done to repair a boot problem, and so destroy the special MBR in the process.  Naturally, if you have ever had to replace the original hard drive you will also be missing the PC Restore feature as you get only one from Dell, and they do not keep an image of the one delivered with your computer. If you have sufficient interest you can check out Dan Goodell's page on Dell PC Restore.  He has given the most complete description of Dell's PC Restore that has ever been made available.  You find that here:  Inside the Dell PC Restore Partition.  My own opinion is that it is nearly as much work to get a broken PC Restore feature repaired as it is to just install Windows from a disk, but it is possible using the information found on that page.
I am unable to access DELL PC Restore on my Vostro 400 using Ctrl + F11 during startup.  Is there an alternate approach?
DELL PC Restore