The middle light keeps flashing 7 times then stops

This mean multiple ink tanks of the same color installed or Ink tank in a wrong position.Check your ink tanks.This ink tanks has a memory chip.Sometimes this chip fails.
If the green light blinks with a orange 7 times this mean the waste ink tank is full.Follow this:
1. Turn off printer
2. Hold down Resume button and press Power button.
3. Keep holding down Power button and let Resume button go.
4. Press Resume button 2 times then let BOTH buttons go.
5. Green lights will flash and then stop blinking.
6. When green lights are solid, press the Resume button 4 times.
7. Press the Power button and the printer should turn off, if not, press the Power button once more.
8. Your printer should respond as normal.