This usually mean 1 of 3 things: Either the Handset lifter is not over the speaker, the ring sensor is off, or the ringer sensitivity control is turned down.
1) If there is no ring then it could mean the ring speaker on the phone is not directly underneath the lifter. In order to detect the ring, the lifter's sensor must be directly over the phone's speaker. Try repositioning sensor (4) by sliding it up or down. If it still is not over speaker, then you must use the external ring sensor. The ring sensor plugs into the back of the lifter and then sticks down to the phone's speaker, wherever that speaker happens to be.
2) The ring sensor is off. You can tell if the ring sensor is off by checking the indicator light on top of the lifer (5).
If the light is flashing, this means the ring sensor is OFF (the liter arm must be in the down position to check this, so the headset itself must be turned off before you can proceed. You can tell if the headset is turned on by looking at the same indicator light on the lifter. If it is solid red that means the headset is on). Turn the sensor on by pressing the on/off button (8), the light should stop flashing when you do so.
3) The ringer sensitivity control is turned down. If the ring sensor is ON (meaning no red light is flashing when the lifter is in the down position) and there is still no ring then you should adjust the ringer sensitivity knob. Its the knob on the back of the lifter with a picture of an arrow going around it..(9)
Turn the knob towards the arrow to increase the sensitivity.
The vast majority of office phones have different ringers! And if the RHL1000 is not detecting an incoming call, even when they are using the ring detector, it could be the type of ringer it is! It can usually be changed, have them look in the manual or look it up online. You can also try cleaning the speaker and the underside of the RHL1000 (where the microphone is located) with a can of compressed air.