I recently bought a TomTom Start 25, only having used friends' satnavs from the passenger seat at their request.  I tried to start it up on Thursday 5 April but it seems to have been "Waiting for a valid GPS signal" ever since which has made it unusable for three days, although three or four times it has randomly updated my location to somethere else I passed through some time earlier.  At the moment, having updated it from my PC, I'm sitting in SE England being told I'm in the Midlands.  How do I get it to function?

By the way, I'm impressed with all the serial numbers etc provided by other enquirers.  I have no idea where to find mine.  Any clues please?

Thanks in advance for any help.