Parallel Set indicates that the CS5121 thinks that another extension is in use on the phone line. First check that no other phones are off their hook. (I have a few that can be tricky to hang up.) If you have no other extensions or if they are on hook, then you need to check if the problem is with your VTech phone or with your phone line.
For diagnostics, I like to use an old corded phone. First try a new telephone cord (RJ-11) to the base of your CS5121. Then if the problem persists, try the new phone cord with the test phone. Listen for a normal dial tone. If you hear a fast busy signal or no dial tone, try the test phone at a different jack on that phone line (if you have one). If you still do not have a normal dial tone, find where the telephone service comes into your building. Open the service box and identify the type of connection. If you are lucky, the service box has RJ-11 jacks. Try your test phone there. If you can't test the phone line or the problem persists, contact your telephone company. They will test the line and repair any outside problem for free.
If it is an inside wiring problem, inspect the wires that are in the open for damage. If only one jack is the problem, open the face plate and check for loose wires. There are two types of connections in telephone faceplates: screw terminals or punch down jacks. The wires need to be stripped (enough to go under the screw) and then secured by the screw for the first type. For a punch down jack, you will need a tool to secure the wires. The tool is available at many home improvement stores in the wiring section. See
http://www.lanshack.com/wire_phone_jack.aspx for the wiring order for an RJ-11 jack. If the problem is inside the wall, you may want to get a professional to fix the problem. Your telephone company will do this for a fee. If you have a DSL filter as part of your phone line, you may need to replace this. (At my house this is part of the outside wiring and gets fixed by the phone company. My sister has the filter as part of the inside wiring and has to fix it herself.)
If only your CS5121 has a problem, try removing the battery pack from the handset. Next unplug the telephone cable and the power adapter from the base. Unplug the power adapter from the wall outlet, as well. Wait a few minutes, then reconnect the power and phone line cord. Then reconnect the handset battery. Test your phone again. If it still gives you a problem, contact Vtech for service if it is under warranty. These phones are not user serviceable.
I hope this helps.
Cindy Wells
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