Hard Disk not found

Hi I am having a problem

My computer has worked for ages, but one day it had an error. A system file(can't remember which) was deleted from the system. Auto repair couldn't fixit. I decided to use the back up disks. I had backed up all important info on flash drives. I chose to delete all data on system prior to reboot. The final percent took 3 days to load. When it was done, I restarted the computer. It now says every time :

internal hard disk drive not found

 to resolve this issue, try to reseat the drive.

No bootable devises--strike F1 to retry boot, F2 enter setup menu, F5 enter PSA

Whenever I try to reboot, it fails. The hard drive disk thing always fails the diagnostic. It never lets me do a backup anymore. I have reseated the hard drive many times, to no avail. The computer is about 2 1/2 years old and has been dropped much. It has had many similar problems in the past, and the 500GB drive has a strange bump. It is Dell Inspiron 3520, if any more detail is needed tell me. I need to know if the hard drive is shot.