Impact Trauma
Physical external trauma can damage the sensitive internal components of a hard drive. Further damage can occur in SECONDS if you reboot. If you can’t afford to lose the data, don’t power up.

Impact Trauma (dropped, run over) — physical damage, unusual noises (clicking, grinding, scraping), drive not recognized, drive won't spin

What to Do
Turn off immediately and DO NOT reboot.

Trauma can damage the read/write heads and media surface, cause misalignment, and at worst, a head crash.