TomTom One GPS fault
I had the same problem after downloading the latest maps, the unit was slow to boot up and would not find any satelites. I had no response from e-mails to Tom tom tech support and I was going to give up and buy a new device if this fix failed. I had tried paper clip resets and resetting to factory settings but they had not worked.
After reading the previous answer to this link I searched Tom tom support for 'clear flash' and the search results were more useful than the FAQ on the normal support pages.
I used Tom tom home to uninstall the current software application and then reinstalled the latest version (I had to go through several updates as my version of the software was from when I purchased the unit in 2007), I then downloaded and ran Clear flash and made sure that I disconnected the tom tom from my PC using the correct procedure (using the eject button in the bottom of the tom tom home screen as I read that this could have contributed to the problem in the first place).
After another reset the device came to life and after a few minutes searching for satelites outside the device worked as it should (try checking the configure GPS option if it is taking a while to find a signal, it could be just me but it seems to speed up the search process).
Hope this helps.