Some of my telephones will read "Line In Use" when the phone doesn't detect a dial tone. I like to use an old wired telephone to check whether the problem is with the cordless phone base or the phone line wiring.
First plug in the test phone and check for a dial tone. If there is no dial tone, try a different RJ-11 cable between the phone and the jack. If there is still no dial tone, use the test phone at another jack and check for a dial tone. If you have two jacks with no dial tone, find your incoming telephone service box. If you have a relatively new phone service installation, the service box will have RJ-11 jacks. Plug your test phone into the jack and check for a dial tone. If there is still no dial tone, contact your telephone company. They will repair an outside wiring problem for free. If the service box doesn't have an RJ-11 jack, you'll need to ask your telephone company to test the phone line for you.
If there is a dial tone at another jack or at the service box, you have an inside wiring problem. You can check for loose or broken wires inside of the jack. Most use either screw terminals or a punch-down design. For the screw terminals, strip another section of the unbroken part of the wire, if needed. Secure the wire under the screw. For the punch-down terminal, take off the cover. Then you'll need a tool that is available in most hardware stores in the electrical wiring section. Do not strip the wire; just place it over the correct place in the terminal and push it into the contacts with the tool. Trim off any excess wire with a small pair of small wire cutting pliers, if the excess wire is blocking the cover from fitting back onto the terminal. http://www.lanshack.com/wire_phone_jack.aspx
has a good diagram of the wire color and pin assignments. If the wiring is okay at the jack, you'll need to check the rest of the wiring for problems. Since the broken wire might be inside the wall, you may want to have a professional check it out. Your telephone provider's technicians can do this for a fee. If you have a DSL computer line, you should check the DSL filter. If the filter is inside at the jack, you'll need to replace the filter. If it is out at the service box, your telephone company will do the replacement.
If there is a dial tone at the jack with the test phone, check the purchase date on the L401 system. If it is under warranty (1 year usually), contact Motorola. Otherwise, replace your Motorola phone system. It's generally not worth the minimum repair and shipping costs.
I hope this helps.
(I've had dial tone issues after lightning strikes (the DSL filter was damaged), mice eating wires (buried phone line) and due to county road crew/contractors who dug too close to the wire. The first two problems required phone calls to get a technician to fix the outside line. The last one gets fixed by the contractors/phone company as soon as they can.)