Charles & Sandra Cohen
Disconnect the head from the body, or (if you're using a head-to-body cable) disconnect both ends.
Clean the gold-plated contacts (gently but thoroughly) with alcohol and a Q-tip.
. . . If the test works, you're OK.
. . . If the test doesn't work, do a "factory reset".
If it still doesn't work, something is really wrong.
. Charles / VA7CPC