oops - should have specified that too...
Yeah, the little pin-reset button on the bottom. Done that millions of times. Had a read on the net to see the reset procedure, and tried them too in the vain hope that it'd make some difference. Nothing.
I've opened up the TT tonight to have a look inside. I've disconnected the internal battery hoping that it'd wipe any form of internal memory/flash or something.
There is actually a small push-switch inside the TT, on the left hand side, that doesn't seem to do anything, but doesn't make contact with the case (so it's not an "intrusion" type switch)....
It's almost like the chipset is getting into a state, too hot or something and freezing, and takes several hours to sort itself out.
I'm going to leave it switched on (at the boot screen) now all night, to totally kill the internal battery, see if a full charge tomorrow makes any difference!