Heres the Order I check things when I encounter this problem on all models
1. If possible before it locks up try and get to the GPS stats screen. (Tap Signal Bars > Tap Signal Bars again on the Route Overview Screen)
If the yellow and black circle in the top left corner of the screen is not spinning it is an Antenna\Motherboard fault causing the Problem and the unit is pretty much toast.
2. If thats OK then it may be the Internal Memory failing. I use a program called HDD Regnerator to check this. If HDD Regenerator reports "D - Delay" or "B - Bad Sectors" The Unit is Toast unless you have a model with a Card slot that can run the whole Navcore and maps off
3. If both these things check out only then do I Low Level format the Device using THIS after which I format it again in FAT32 via Windows Format and reinstall the Application software again using TomTom Home.
4. If that still does not fix it I then Check the Boot Voltage of the battery via the hidden Diagnostics screen. To Access this after turning on the TomTom, whilst it is on the boot screen press the Power button briefly again. If the battery boot voltage is low (3.5v or less) on a fully charged battery then this could be the cause. In this case I then pull out the battery and power it up on USB power only and see if this fixes it if it does then get a new battery.
5If none of this fixes it then it would be something shorting on the mainboard most likely. Hence its good for spares only.