I have a couple of suggestions.
First, remove the battery from the unit for 3-5 minutes then give it a try.
Second, if your's is a touch screen model, are you moving the Lock switch to the "Locked" position?
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Have PV-500 & willing to travel.
"Answers are easy. It's asking the right questions which is hard." (The Fourth Doctor, The Face of Evil, 1977)
"Somedays you're the pigeon, somedays you're the statue.” J. Andrew Taylor
"I have never met a man so ignorant that I couldn't learn something from him." Galileo Galilei