Phone will call out but will not accept calls.

If your phone service is backfeeding into you home phone wiring, there is probably a short or open in your home phone wiring.  You could set up a cordless phone system with the base station near your  modem and place the remote phones as needed.  That way you bypass the home phone wiring.

I do have a security system that uses my phone line to call out now that you mention it. I hadn't thought about that being the problem.

I have a solid light on Tel 1 and I don't use Tel 2.  All phones have been tested and work fine when hooked up to the telephone 1 port in the back of the modem. Comcast sent two technicians and they said it was one of the phones but that is not the case. It has to be in the home wiring. Technician did not go to the phone box outside but I don't think there is any kind of signal going to the box. Our neighborhood did recently upgrade to fiber optic cable and the problem began around that time. I have no idea what to look for if I do open the phone box outside. Also, I can not find anyone in town who works on household phone wiring.

Where do I begin to troubleshoot the problem. I have called around and it seems no one works on household phone wiring anymore. Comcast says that home phone wiring is my problem. Comcast actually hooked up the phone to backfeed into my household jacks but now don't seem to want to fool with troubleshooting. 

I plugged each phone (3) into the modem and all three worked which makes me think it is not the phone.

I honestly can't remember what I did to correct the problem. I wish I could help.

Just recently, I've been able to place calls but can't receive them.  Callers continue to get ringing even when I answer (and I only get silence).  There are two ports on the back of my modem.  I switched my phone line to the other phone port and I'm now able to receive calls.  I've had this modem about a year now.  I guess ports can go bad???  Anyhow, maybe this will work for you.