Have you performed a full power cycle and left the system off for 10+ minutes? I Would do that
While the system is off, ensure the power supply in use (7V) is connected to the power cable fully and that the wiring has not come loose. If you have a multimeter, check the power to ensure it is producing the correct voltage.
After confirming power is connected, and waiting 10+, power up the panel battery first, then power supply. Turn on the panel by holding the button on the side down for about 5 seconds. Does the panel boot up or do you continue to get the blinking red leds ?