Reset button on 910 ???
Before you reset your 910, first make sure your battery is (well) charged and if you are using an SD card, it is taken out.
The reset button is actually a tiny hole at the bottom / base of the unit.
Simply use a straightened out paper clip or something similar, insert it into the hole and hold it there for 20 seconds or so, until the device turns off. Then push the ON/OFF button and hold it down for a while ... (5 seconds ... or lots more) until the device powers up again. If you're using an SD card, you can then insert the card (when it is looking for it).