The TRU8885 has a Do Not Disturb feature which will disable the ring on the base and all handsets. To toggle this off, press and hold the DND button on the base. (The key is on the lower left of the keypad, next to the * key). The answering system will turn on when the DND feature is enabled, if it wasn't previously on.
However, this shouldn't disable the dial tone when you call out. I suggest that you check that the base has power. After that, you have to look for a wiring problem. The problem could be the phone, the RJ-11 cable between the base and the wall jack, a wire that is damaged in the wall, or an outside line problem.
First try a new RJ-11 cable; make sure not to use a wired handset cord. After that, I like to use an old corded phone that requires no power adapter to test the line. If the test phone gets a dial tone, then the TRU8885 base has a problem. If the test phone doesn't hear a dial tone, try plugging it into another jack on the phone line if possible. If there's no dial tone (or no other jack), find the incoming service box. If there is an RJ-11 plug in the box, check for a dial tone there.
If you have no dial tone at the service box or can't test the line at the box, contact your telephone company. Most companies will check the line and fix outside problems for free. If the problem is at the first jack, remove the cover plate and look for a loose wire. There are two styles of RJ-11 jacks. The screw terminal type require you to strip the wire and secure it under the correct screw. For the keystone jack type, you do not strip the wire. You use a punch-down tool (available at many hardware stores in the electrical section) to push the wire back into the correct section of the keystone. The little pins will puncture the insulation when the wire is properly inserted to make the connection. See http://www.lanshack.com/wire_phone_jack.aspx
for the connection wiring connections. If you have an DSL filter inside your home, replace it if it is faulty. For any other inside wiring problem, you may want to let a professional find the wiring break in the walls. Your phone company will do this for a fee.
I hope this helps.
(I have had dial tone issues from several different causes. A single jack's wire was left disconnected after a service upgrade. Several outages were from damaged outside wiring either from mice chewing or a contractor digging through the wire. With a DSL line, the lightning strike damaged the filter and blocked all of the signals. Recently, a fiber-optic service card failed resulting in intermittent dial tone failures. Except for the first issue which I could fix myself, the local phone company or appropriate contractors fixed the issue for free. However, I don't live in an area where the phone company is trying to stop serving some wired phone customers.)