Thanks........it reboots constantly whether anything is connected or not.
I think it is likely to be failed firmware upgrade or some such thing. Or just a configuration issue.
A configuration issue would not cause continuous restarts of an electronic device upon power-up initialization. Usually that means the device is 'broken', and is restarting only as a last-resort. (It should be a last-resort by design - upon startup a device is supposed to start up and stay started up.)Otherwise, on reviewing the answer I offered late last year, I stand by what I said: the switch is most likely defective, period. If it has a parts warranty, then I advise replacing the main control-circuitry board inside it.
(And as an afterthought: before replacing anything, pick it up bodily after powering it Off, and shake it as vigorously as you can, without dropping it, listening for any noise inside it. If anything rattles inside it, or makes any sort of metallic noise, open it before getting any parts and find out whether a loose paper-clip or other metallic debris such as staples etc., might be loose inside it. If so, by crossing two connections, that could cause your problem.)
Thankfully it has become a little academic - DELL have agreed to swap it out and the unit is arriving Monday.
Thanks again, Andy
Happy to leave a positive rating etc..