Thanks all: In sequence:-
Keef - now how did you know it was a Maxtor? The bane of my life. Several (documented here) disk failures over the years. Not sure ALL know, but despite the reseller giving a 12 month guarantee, Maxtor (used to, anyway) give 5 years. This one is one of the free replacements and was sitting idle on the 'puter.
Damn thing just goes from 76GB'ish NTFS 'drive xx' to not there and no status.
Saab - yes, separate power. I connect IDE then power then USB to desktop.
stickyb - USB2 but sole occupant of FRONT conector. Will try the rear one. power is ok and write c off.
Standby a while.
Still comes on line as 'Basic'/'Online'/Healthy' and then disappears after a minute or two.