Ok, here is the description of the support:
Please try a forced firmware reinstall.
This is done by loading the firmware onto a formatted USB drive, outside of any folders including the AHQU folder.
You then insert the drive into the USB A Qu-Drive port when the mixer is powered off.
Press and hold the USB and HPF In keys whilst powering on the unit. It will then show this same behaviour and, if it loads the firmware successfully, it should eventually boot.
If this doesn’t solve the problem, it is likely a hardware issue.