If no connection is established at all by the BGAN terminal, the issue can be related to GPS acquisition. GPS acquisition is a very important part of the registration process with the Inmarsat network, and without a GPS fix the BGAN terminal is unable to register.
GPS is taken from the GLONASS satellites. If the terminal is struggling to get a GPS fix on the first registration, point the antenna straight up into the sky until it gets a fix. Once the terminal has acquired a GPS fix, you should be able to connect to the Inmarsat network.