I managed to brick one of my Netgear M5300 switches while trying to factory reset it, by selecting "Erase permanent storage" from the boot menu. At this point, it displays 'Uboot M5300 VerNo=184.108.40.206' on the console and does not progress further.
To recover, get a FAT32 formatted USB drive, and save the firmware as 'boot.stk' on it.
Insert the drive into the switch, connect to the serial console and power up the switch.
Interrupt Uboot by pressing Q. You should get a '=>' prompt.