There may also have been a BIOS conflict of some sort - I recall that Thinkpads are slightly weird and store some firmware in the normally-unused space at the start of the disk. This disk was indeed an ex-Thinkpad one which also has a hidden partition for the Rescue & Recovery feature, and given that it was last used in that laptop in 2008 these may well have been older than what the BIOS expected. I do know the laptop was reluctant to boot which implies the BIOS was trying and failing .
I'll just have to try another hard disk at some point. It's not like I've got a shortage of them... over the years I've accumulated a lot of random computer spares, a lot of which is now massively obsolete these days (anyone need an ISA 56k modem, a brace of PC100 DIMMs, an AGP graphics card, or a 3GB laptop hard disk?). I've kept it mainly because I don't know where half the stuff is (it's managed to spread itself around multiple crates both here and at the parents'), but also because every so often some piece or other comes in rather handy.