DIAGNOSIS The lid's locking pin or the handle mechanism is blocked by the pot's rim, usually because the lid isn't aligned perfectly or there's debris in the way.
FIX Don't force it. Open the lid fully. Look at the underside of the handle where the locking mechanism is. There's a small metal pin. Make sure it's not stuck. Now, place the lid back on the pot, but before trying to turn it, ensure the arrow/triangle on the lid is lined up directly with the unlock symbol on the pot's handle. It needs to be *perfectly* aligned. Then try turning clockwise.
IF THAT DIDN'T WORK Inspect the rim of the pot and the inner groove of the lid for any small bits of food, grains of rice, or mineral deposits (hard water spots). Even a tiny obstruction can prevent the lid from seating deep enough for the lock to catch. A soft brush and a wipe-down should clear it.
HEADS UP Never, ever try to use the cooker if you can't get it to lock properly. The multiple safety systems are designed to prevent operation without a secure lock. Forcing it can damage the mechanism.