I would try ringing your number from another dterm display phone first as suggested above but it is possible to set the key not to ring in the system programming. When you get cat mode in the display press lnr/spd you will get command in the display. dial 9001 press recall, dial your extension number, press trf dial the key number your line appears on (if it is the top left it is 01 if bottom right it is 16, press recall it should display a 1 if the button is supposed to ring. if it displays a 0, that is your problem! dial 1 and press conf if it accepts it then you may need to save the data but if it comes up with password required, you will have to get IT to make the change. If you are on an IPS and it accepts the change, it has to be written to memory (an IVS or IVS2 doesn't need this step) press lnr spd again to get the command prompt, using the line keys (01 ia A 02 is B etc) enter EC6 press recall it should display a 3. dial 0 then press conf and thats it you can lift and replace the handset to get out of programming mode at any time. If it doesn't accept the EC6 then you won't have to worry about it!
Just a thought with your comment about not getting a display phone if IT replace it. If there isn't another display phone for you to use to dial your own number, you can swap yours with a non display dterm and then dial your number.