You shouldn't have to do anything for it to ring, the default is to ring. Does the OBi212 ring with an incoming GV call? Do any of the LEDs on the OBi212 flash with an incoming landline call? If the LEDs are flashing, can you answer the call even if it's not ringing?
I have an OBi110, so the following might be slightly different.
Check the Line Port voltage. Enter OBi Expert from the Dashboard. Click on the gear ICON to the right of your OBi212 then select OBi Expert Config, confirm and select Enter OBi Expert. Click on Status then click Phone Status.
My TipRingVoltage for the Line Port is -47v
When I disconnect the line port is shows 0v
If you have 0v then you have a bad cord, you're not connected correctly or your OBi212 is defective.
Do you get dial tone if you connect a phone directly to the same jack as the OBI212?