I bought a doro 5030 the weekend when you dial a number you can't hear the phone ring on the other end

SOURCE: Internal Call "Voice Call" and does not ring

You can toggle each individual phone extension as to whether or not it recieves a "voice" call or a "ring-first" call.

At the extension, press "SPEAKER - 60" it will display the mode. Press the * (asterick) key to toggle between the modes. Then press SPEAKER again to set.

SOURCE: Dial Tone but won't call out.

The problem was the main phone line not the phone itself

SOURCE: can't dial out or receive calls

constant dial tone and cant dial out or receive calls

SOURCE: no dial tone - phone rings for incomming call but I can't hear or talk

This can be a problem with your handset.
Have you tried a different phone in that same jack?

SOURCE: No dial tone at my end when I ring a certain number even though the number I'm calling is ringing, also really slow to connect. all other numbers are fine

dial tone but mobiles ahve no dial tone when making or receiving calls.....