There are threads on here and on seabreeze explaining what to do. Option 1 is to leave until it discharges, problem is the battery seems so good on this compared to a mobile phone for example and it can take a long time.
Option 2 is to disconnect the battery. Bear in mind this will void the warranty so if you can take it back to where you bought it then do so first of all and get it replaced.
If not then unscrew the two screws from the bottom of the unit, and all on the back. Take off the back. Unscrew the single screw holding down the pcb board and lift it, disconnect the battery.Reconnect and put back together, be careful to get the rubber trim in place as you put the case back together. Now it will work.
Once that is done update the software to the latest version - http://mtbest.net/setting-up-navi-GT31.htm Which is supposed to stop the freeze. Another thing to try to stop it ever freezing is to give it a discharge by leaving it on every now and again until it turns off, then a full charge. (remember to do it when there is now wind forecast for a few days and it is guaranteed to change the forecast ;-)) Mine only ever froze once and I took it apart to fix as it was over a year old.
Locosys replied to me after 2 days and were very very helpful, they gave me lots of things to try but we couldnt get mine to work. It has had a good life and is now in my spare parts bin. Now have a replacement.