I like to use an old corded phone to diagnose telephone line problems. First though, try a new telephone cord between the base and the phone jack. (This can be obvious to some but I once saw a person swap a handset cord (the coiled cord) and an RJ-11 cable.)
Next plug a different phone into the jack. If it gets a dial tone, the KXTGA470B needs service. (If it is out of warranty, it may be better to replace it.) If the second phone does not get a dial tone, try the spare phone at a different jack if there is one. If the phone gets a dial tone at this jack, your wiring to the jack or inside it is faulty. I'd check the jack first, unscrew the faceplate and look at the back of the unit. There are two types of jacks. One has all of the conductor wires connect to screw terminals. If any wire is broken, strip the shielding from a bit more of the wire. Then wrap the wire under the appropriate screw. The other type of jack is a keystone. If a wire is loose, you'll need a punch-down tool (available at many hardware stores in the wiring section). Do not strip the wire, just press a new section into the correct point on the keystone. See http://www.lanshack.com/wire_phone_jack.aspx
for the pin assignments.
If there isn't another phone line jack or there is no dial tone at another jack, find where your telephone service comes in. Open the box and look inside. If you are lucky, the service will have an RJ-11 connection. Plug in your test phone and check for dial tone. If there is still no dial tone, call your phone company and tell them to fix it. (I've had mice chew wires in underground service.) It will be a free repair. If there is a dial tone here, you've confirmed an inside wiring issue. One thing to check while you are at the box: since you have multiple jacks, check that all of the wires connect to the box. We had our service upgraded and they forgot to wire one jack to the new service box. (It was obvious when we went to the box; the wire was just floating behind the house's vinyl siding.)
Next consider your service type, if you have DSL with your phone service, check the filter. Some phone companies have these inside the home and you are responsible for it. Lightning strikes nearby can damage them and interrupt the phone line. Otherwise, since you didn't see any breaks in the wires when you inspected them, you may want a professional to check the wiring. It's possible to have one broken conductor within the shielding. (One way to test this is to swap the wires at the service box and the jack. Most RJ-11 lines are 4 or 6 wires. Two wires are needed for each line. Use the diagram I linked to above and physically connect the R2 and T2 lines to the R1 pins.) Some telephone companies will do indoor repairs for a fee.
If the service box doesn't have an RJ-11 connection or you have an outside DSL filter, ask them to send someone out to physically check the service. (Just because their computer says it is up, doesn't mean it is. I've seen it happen.)
I hope this helps.
(My preferred test phone is an old rotary unit. It never fails unlike some newer phones.)