DIAGNOSIS If the float valve (the little silver pin next to the lid handle) doesn't rise, pressure isn't building. The usual culprit is a bad seal, either from the ring, food debris, or the valve itself being stuck.
FIX Turn off the pot and quick release any potential pressure (carefully). Open the lid. First, check the silicone sealing ring. Remove it, wash it, and make sure it's not twisted or pinched when you snap it back into its groove. Next, check the float valve hole. Use a toothpick or a pipe cleaner to gently clear any tiny bits of food or starch that might be blocking it. Move the valve up and down with your fingers to ensure it's not stuck.
IF THAT DIDN'T WORK The lid might not be fully closed. Align the arrows on the lid and base, then turn the lid to the locked position until you hear a distinct beep from the base (on some models) and the arrow points to the lock symbol. If it's not fully rotated, it won't seal.
HEADS UP It can take 5-10 minutes of heating for the valve to pop up, depending on how much liquid and food is inside. Don't panic if it doesn't rise immediately after you set it.