Adding on to Joe's comments...
Every digital probe goes south sooner or later. Usually it's the result of moisture in the probe itself. Whenever I see 'em on sale on sale at Wally world, I buy 4 of them...$13-$19.
Your best insurance is a Thermapen. Very accurate and you'll have a readout in seconds. They're on sale right now.
HERE'sthe link. I've owned one for 4 years...never had an issue.