Ok, there are a couple of options that may or may not work. The problem with
TomTom units is that they do not like being used with universal chargers and sometimes they can be damaged when using one. The hard disk drive inside them in particular is very sensitive.
Try these options first before thinking about having the unit repaired -
Try holding the reset button for anywhere between 1 and 20 seconds.
Try holding the power button for at least 3 seconds
Lastly hold down the reset button for 10-15 seconds and then while holding the reset button, press the power button and hold that for around 5-10 seconds.
If you are unsure of where the reset button is, here is an image showing its location -
If none of the above steps work then it is highly likely that your unit has suffered damage that needs to be repaired by a specialist.
I hope this helps and thank you for using
FixYa