The reader is not sensing the probe. Typically, the meter must be sent in for service. However, there is one cause for which it may be possible to get the meter functioning. Remove the face plate from the top of the display. You should be able to see where the 3 wires from the cable that feeds in from the probe connect to the circuit board. If one of these wires is obviously loose, you can try to re-attach it. Otherwise, contact Spectrum Technologies or your distributor to obtain an Returned Merchandise Authorization (RMA) form.