The red solid light is the power LED.
The 4 blue (blinking) lights, one for every ESC of the 4in1 board, are status LEDs.
If they are blinking fast, the ESC does not get a connection to the FC. (In this case check the 8pin cable and connector if you use it)
If they are blinking slowly (every 2 seconds) it fails in selftest and the ESC is damaged.