New
#11
Sorry John - yes, I didn't get round to doing all the USB ports as I meant to and then I forgot about it (only reading the latest answers in the thread) - but I just found what surely must be the problem: I said above that there were no yellow or red flags in the Device Manager, and that's true after the freeze clears. However, I just managed to get Device manager open during the freeze-up, and under System Devices, the 'AMDA00 Interface' entry has a yellow exclamation mark against it. When the freeze-up stops, all the entries reload and the yellow ! disappears.
I am not sure what that entry is as I write this, but will Google tomorrow (need to get to bed now, 1.30am). Presumably it's a software rather than hardware issue (though I could still get down under the desk and try juggling all the USB connections. Is that likely to help now??). Meanwhile, maybe the problem (and solution???) is now clear to someone more familiar than I am with what this implies in practical terms.
Thanks again.