I suspect that the hard drive was damaged during the fall.
Try these free diagnostics to verify that: HD Diagnostic
(read the details at the link) - Test ALL
of the hard drives.
Also, you may want to try reseating the drive. To do this:
- unplug the AC Adapter and remove the battery
- open up the part of the case that covers the hard drive.
- remove the hard drive (there may be additional screws to remove, and then pull on a plastic tab to disconnect the drive).
- push the hard drive back in firmly.
- replace all screws, replace the battery and AC Adapter and try to boot.
- you may want to try Startup Repair also: Startup Repair
If that doesn't work (and if the hard drive test above fails), then you'll have to replace the hard drive and reinstall Windows. Most Dell's come with a Windows 7 installation disk. If you don't have that, then please contact Dell for a replacement: Order Recovery Discs (USA)