Have the same issue, boot screen is visible and nothing happens. Have tried anything to connect via Cura (even with version 15.x which allows to setup a COMM port), but Cura is unable to connect.

I tried all firmware versions listed above with multiple SD cards. No success (and this is what I expected).

I turned off the machine after 4 hrs of printing just 1 min after the print job got finished. I guess, the MB died due to thermal stress after I turned of the machine which also turns of the fan blowing over the MB. I also recognized the the ribbon cable for the left X/Y stepper was routed in front of the fan cooling the MB. I would say it lowered the efficency of the fan by at least 50%.

Hey Creality, please leave us feedback and come up with an real investigation and a solution for your customrs. This firmware reflashing approach is nothing else than a straw. My patience is low due to bad experiences in terms of warranty with chinese companies. Thats why I don't buy anythig from your country without Paypals buyers protection