This happened to me. It took three shutdowns to make it work again - I had to do the firmware update 3 times. On the final time, I just left it alone for a long time - way longer than expected, and it suddenly started back up by itself and completed the update.
Hope this works for you.
So I've had my brick now for 3 days. I can't fly - at all - because of the restrictions DJI has placed on the device.
Chat says to email support. Support says to fill out a form. There are 3 forms. none of them are mobile enabled, so you have to do it prior.
And now I hear that you have to...