LINE 3 RINGS ON ONE PHONE- AND DOES NOT RING ON THE... (by 2 users)

INCOMING CALLS THAT COME TO LINE 3 WILL RING ON ONE PHONE- THERE ARE 3 OTHER PHONES IN OUR OFFICE... THE LIGHT BLINKS ON THEM, BUT NO RING...AND YOU CAN ANSWER IT BUT I CAN'T PHYSICALLY FIGURE HOW TO SET THEM TO RING...IM HOPING SOMEONE ONE CAN HELP ME ! :) We have an NEC 32 line Electra Elite that I cannot figure out how to make one of the phones ring. The only one that rings is my phone and if I'm not here, no one else can hear it. I have the User Guide but it is not very helpful.