I went one step further: We had an old HP-UX machine with a failed hard drive that wouldn't spin up. The data on it wasn't supercritical but still nice to keep,

I went one step further: We had an old HP-UX machine with a failed hard drive that wouldn't spin up. The data on it wasn't supercritical but still nice to keep, so I was free to experiment. I removed the housing and pushed the platter by hand. It spun up, and while still open, I immediately took a full disk image with dd. A more similar story to yours was with my 120MB hard disk on my PC when I was a, which inconsistently exhibited similar symptoms. I had no money, so always had to do with what I had (many stories sprang out of that). The hard disk was in a removable caddy, and when it refused spinning up, I simply took it out of the PC and gently bounced it on my bed right next to the desk. Put back into the PC, it then worked every time as I recall.