One of my S3 got bricked during firmware update, browser just crashed randomly. How do I fix it?
What actually happened -- power failure during flash or something else? If something else, then what and wired LAN or wireless LAN?
In any case, the only thing we can try without Bitmain intervention is resetting via the button to immediate right of the RJ-45 connector. If it can't be reset, then the FW is damaged and needs technical assistance.
PS. It's recommended never to use a wireless connection for flashing equipment. Too much likelihood of dropouts.