Like several others have said...
Disconnect from the phone jacks all of the phones, computer modems, answering machines, fax machines, Sattellite TV boxes... everything in the whole house that connects to the phone lines first. This eliminates a lot of variables. Then take a known good telephone to the DEMARK location outside your house, like you already did, and test it. If it works there, take it to each the phone jack in the house and test it at each one. This is where a cell phone comes in handy, as you can call yourself to see if the ringer works. If all of the jacks are OK, then start plugging the phones, computer modems, answering machines, fax machines, Sattellite TV boxes back in, one at a time, testing each time until you find the culprit. Don't be discouraged if everything works and there is no problem. Sometimes, as mentioned by others, if things are disconnected from their power source for a while, they will start working again. Have a great weekend and please let us know what you found.