There are several different kinds of resets, which can be found in the manual. The manual will walk you through the hard factory reset, which can be found here http://download.tomtom.com/open/manuals/...-Sport/refman/TomTom-Runner-Multi-Sport-RG-en-gb.pdf
If the screen does not appear damaged and you have been trying to charge it, then it could be your battery. First, this could be your charger. Your charger may no longer be working so you could try purchasing a new charger. If your charger had been working, then try a hard factory reset, which can be found in the manual. If the charger and hard factory reset doesn't work, then it probably is the battery and will need to be replaced.
There are several reasons your watch may not be picking up signal. First, if the icon continues to blink that's because it is trying to find signal. Try moving to a clearer area so that the GPS signal can connect. If this doesn't work, then make sure that the watch is securely strapped to your wrist with the screen on top of your wrist. If the band is loose and the watch is loose on your wrist, then this could interfere with the signal and cause signal loss/interruption.