Try resetting the tomtom by iserting a paper clip or similar into the reset hole underneath the unit. Be carefull it only needs 1 little push , you should feel the reset button click as it's a tactile switch. Do it gently as it wont take repeated pushing . if that doesn't work you have either a software fault of files that are or "used to be " on the SD card or a battery that is on it's way out. If the same thing happens with a power supply connected then you can be sure its a software fault. try reinstalling the files back onto your SD card ( you did make a backup copy of your SD card , didn't you ? ) . if you don't have a backup then things are going to be difficult for you. there are ways and means to recover but its not easy to describe here.