Is it possible to access the files on a tomtom even if it won't switch on (possible wrong bootloader) and is it possible to save it

Maybe your baterie is dead?
Connect to charging and try again?

Please make a complete posting including all the details, otherwise it is just a quessing game here....
Include the model, Navcore and what you have done prior to the problem.

Not 100% sure what navcore has been used. The tomtom belongs to a friend. I think he has put the Europe truck 8.398 navcore and map on it with the standard 5.5120 bootloader but, even though the green light on the unit lights up when it's sat in its cradle supposedly charging I am not sure that it actually is so, this weekend I'm going to try and work out whether it is charging and I will post again hopefully with more information as at the moment I am working away from home. The model is a go 910. Thanks for getting back to me.

Try with reset button, sometimes happens with this model.
In my company was over 100 pieces of GO 910, everythime when don't wan't to turn on we have restarted the unit and was everything OK.
Maybe is som other problem, this advice is from my experience!