DIAGNOSIS That's the Vortex telling you it can't read the temperature inside. The most likely culprit is the cooking pot not being fully seated and twisted into the locked position.
FIX First, turn the unit off. Lift the cooking pot out and then place it back in. You'll feel it drop into place. Now, grip the handle and give it a firm clockwise twist until you feel it click and lock. The icon on the display should switch from the unlocked symbol (an open lock) to the locked symbol. Try your function again.
IF THAT DIDN'T WORK With the unit unplugged, check the small temperature sensor probe in the center of the base inside the unit. Make sure it's clean and not bent. Wipe it gently with a damp cloth. A buildup of grease or a bent probe can mess with the reading.
HEADS UP The three-beep error happens a lot when you're in a hurry. Always listen for that distinct click when you twist the pot. If it doesn't click, it's not locked, and the safety system won't let it heat.