I had my house mates dog knock a Toshiba computer off a coffee table a year or two ago. I had extremely similar problems as you've described.
I took the risk and just bought a new hard drive, swapped over and it resumed working as normal. I'd guess most likely it's just damaged from the fall. Down side is I lost anything on the old hard drive though I'm sure if you need important things recovered someone out there could do it for a fee.
