The odd thing here is that incoming calls work! I would power cycle the OBi110 as a first step. Power down for a few minutes, power back up and wait for a few minutes for the OBi110 to go through its boot-up process.
If still no dial tone, then check the readings at Status > PHONE & LINE Status > VBAT. It should show something like: 58v (12.1v).
Also check Status > PHONE & LINE Status > TipRingVoltage. It should show something like: 45v.
If still no dial tone, it's time to submit a ticket to Obihai. I guess after this time you are well out of any warranty period.