Can't lock onto satellite

I have a Mio A210 with TT5, but for the past couple of weeks it just will not lock onto a satellite. There are plenty of bars and it keeps hunting but never gets to "blue" bars. I have another identical PDA which when I put them next to each other the 2nd one has no problem locking onto a satellite.

Any ideas what is happening - its always been fine until recently.

Quite often a full clean re-install will cure the problem.