In quiet room, move the magnet back and forth past the sensor. You should hear it 'click' softly as the magnet passes. If it does, re-check batteries, then if it still has no display, it may be time for a new unit.

BTW I used a wireless until I found out it would not work while my Niterider MOAB HID headlight was on. Switched to an Astrale 8 with cadence, and have had no issues since.