There is a Mode switch on the rear of the G2, under the rubber cover.
To pair your phone/tablet/computer with the G2, the mode switch must be set to 'A' (left position, if looking at the rear panel).
It should be set to the 'A' position as default, but it is possible that it could have been changed to the 'B' setting, which could be why you cannot pair with the G2. Please make sure that the Mode switch is set to the 'A' position to pair your Bluetooth device with the G2.
More information on how to set up and pair with the G2 can be found in the video below: