I believe you are referring to the PWR LED showing RED light. This means the AP is in boot process.
If it is stuck in boot process for longer duration, try doing the below steps: 1. Disconnect the AP from the power source for 60 seconds and then turn it ON. 2. Make sure there is enough power has been supplied to the AP. 3. Try using a different cable and different port in the switch. 4. Try doing a Factory reset on the AP.