When you say you wiped the drive, was this just a free space erase? If it was, I don't see how it could be the cause of your problem.
There is a good chance that the laptop screen is indeed disabled rather than non-functioning, and that you have an issue with your video driver. Does XP boot to the external monitor? If it does, I would use that to run whatever program Dell provides to restore the machine to factory condition (which is what you want to do in any case); this usually works from an internal recovery partition rather than the installation disks. You can then run a free space erase, which should make doubly sure that all your personal data is gone (I suggest that you un-tick the option to erase cluster tips, as that will give you a load of essentially spurious errors).
If that doesn't work, try the video driver properties. Although computers vary, most video drivers come from one of two companies. I had a problem with an XP laptop not long ago where the drive had set itself to work with the laptop screen only, and would not switch to an external monitor from the keyboard, and I had to change the settings in the display properties. Your problem could be similar.
In the worst case, your laptop screen has chosen this moment to die, and the system is simply recognising that fact. In that case, unfortunately, the machine is unlikely to be economically repairable.
David