Yeah - reset the CMOS by removing all power, batteries, and swapping the jumpers too. (I did put the jumpers back into the correct location!)
Just tried removing all internal cables (except cooling fans for MB, CPU & Case) with no luck, removing external cables as mentioned, and cards, with no luck either.
The cable points had all the correct voltages.
Final solution maybe for the system to take a slow trip to 10,000' followed by a fast trip back to terra firma.
??