Tried 3.7.3 which is the newest 'stable' I think. Didn't do 'make oldconfig' on the grounds that I didn't do it with 3.8rc3 - the one which worked. Same results though. Beginning to have silly ideas like - could it be the nvidia drivers I install
So I copied the config from the one that worked and made oldconfig with that. Ran make xconfig and made sure the srw was enabled. Currently making again. 3.8rc4 is 'out'.
No point installing a 32bit system. It works on the one 64bit one, so it can't be that.
Do you ever feel like there's loads of people following the thread and they're all going "ha ha - I know why it is."?