Thanks everyone.
I've just about kept up with (and tried) all suggestions so far but fiddling with the BIOS takes me into new territory.
As I'm not known as 'Sexy Fingers' for nothing I think I'm going to have to admit defeat and take it to someone who knows.
Might try reformatting and running ME though as a last resort. Won't be for a while though as I'm away on tour from today.
I'll let you know how it goes.