Take an old fashioned phone (wired handset, no external power needed) and connect it to the jack. Do you have a dial tone? If the simpler phone has a dial tone, the cordless phone system has a problem. Otherwise, try a different RJ-11 cord. (Note: a handset cord does not work in place of the standard phone cable between the base and the wall jack. I've seen this mistake made.) I assume that the power adapter wasn't cold when you unplugged it and plugged it back in. (No power to the base would give the same error on some handsets.)
Check for dial tone at other jacks for the same phone line (if available). I use the old-fashioned phone for these tests. Try locating the telephone service box. If there is an RJ-11 jack in the box, check for a dial tone. Your telephone company can test the line if the box doesn't have a RJ-11 jack. If you have no dial tone at any jack, contact your telephone company. You probably have a damaged wire outside. Most telephone companies repair outside problems for free. (There are some companies that will try to get you to pay for an upgrade to new wiring.)
If other jacks inside your home work, then the loose or damaged wires are either behind the face plate or in the wall from the service box and the face plate. Open the face plate and look for any loose wires. There are two types of face plates/jacks. One uses screws to secure the wires. Remove the insulation on each conductor and secure at the terminal location. The other option is a keystone jack. For these, you need a wire push down tool from your local hardware store (in the electrical wiring section). Do not strip the wire and push into the barbs of the keystone at the correct spot. Cut off the extra wire sticking past the outside edge of the keystone with wire nippers if needed. This diagram,
https://www.lanshack.com/wire_phone_jack.aspx , shows the wire colors and the appropriate terminal locations.
If the wiring problem is inside the wall between the service box and the face plate, you may want someone else to track and fix the issue. Many telephone company service techs will do this for a fee.
I hope this helps.
Cindy Wells
(I've had phone issues from mice chewing on the lines (outside, underground), someone breaking a line while digging for another utility, a damaged modem in a fiber-optic service for all jacks for the house. Those were all repaired by the telephone company or other agency. When we had single jack that failed to work following a service upgrade, we found one wire left loose behind the siding. Fishing the wire up and plugging it into the service box solved the problem.)
