Try charging the device indoors with the power off. If the device still won't charge, the device may need new cables to charge. Consider purchasing a micro USB to USB cable and a USB to wall adapter. If new cables are not helping, then the device may need a new battery.
Check out the troubleshooting guide on this device for more information: [[TomTom Go 500 Troubleshooting|TomTom GO 500 Troubleshooting Guide]]