1. At the OBi110, unplug the cable that goes into its LINE socket. Leave the other end plugged in to the wall jack. Try the POTS line in the other room. If it works the problem is probably in your OBi110. If it does not, the cable that you unplugged is probably faulty and you should try another one.
2. If you have the OBi110 plugged in to the POTS line but without it powered up and without any phone plugged in to it, does the POTS phone in the other room work?
3. Possibly the OBi110 LINE section has gone faulty. Have you had any lightning strikes shortly before you noticed the problem?