I viewed the YouTube video.
To me it sounds like there is a gear that is slipping.
Maybe the worm screw that advances and retracts the head mechanism has become buggered. I think there is a metal gear that drives it or vice versa.
You can take the metal shielding off the top (usually two small screws) and test the drive....then at least you might be able to see what is happening to the drive mechanism when it tries to move the read/write heads.
Anyway, it sounds like a mechanical problem to me. Maybe it was something slipped inside it when you were holding it to do the soldering (although normally something like this wouldn't happen).
