Tom Tom 910 Green light but does not come on.

Remove battery and disconnect from power for 5 minutes, also remove map card, this will reset the device. Try it out
click;

Repair4GPS: How to Clean, Upgrade, Repair, Mod, Disassemble a GPS ...

see here

http://www.tomtom.com/lib/doc/legal/lw/LW-English-US%20CAN.pdf

To only way you can fix it is taking apart the Tom Tom, checking if the flat ribbon cable and connector to the screen are well in place and eventually replace the display ($80 on Ebay).
Unfortunately this will invalidate the guaranty, and you risk to damage your GPS if you are not a really experienced DIYer. Tom Tom offer one year full guaranty on all their receivers.
Contact Tom Tom and get it repaired:
Support URL: http://www.tomtom.com
Support Phone Number: 978.287.9555
Support Email Address: [email protected]


Hope this may help;

DON'T FORGET TO RATE:

There is a reset switch but you need to use an opened out paper clip to press the switch which is located next to the connections underneath the unit. The switch is tiny, about the size of the end of an opened out paper clip. Switch the unit of, just press the reset button once and then reconnect/switch on, and the tom tom will revert to its starting routine. It worked for mine.