Just want to confirm that you are talking about a Mini not the
Mini 2 as the only LEDs on the bottom of the MM are the 4 next to the power button. Also not sure exactly what you problem is, Turning on, Registering, Linking.... so here's a couple of suggestions.
To turn on, press and release the power button then press again and hold for 2 seconds. The Mini will twitch the motors. A press and release just lights up the appropriate numbers of LEDs to indicate battery charge . The second press and hold completes the aircraft (AC) powering on. It's the same sequence to turn on the Remote Controller (RC).
Here's how to link the AC to the FC
View attachment 130988
Here's a link to the
Mini PDF Manual