I was attempting to get my BBB to recognize my USRobotics USB modem. It showed up when I entered lsusb, and went through the set serial commands for it to recognize it, but it would not show up as a tty device, after having it connected for about 2 hours, I did another reboot, and the board no longer responded. Only the power light would light up, but none of the others. After doing a bit of research, I believe I ended up overdriving the current through the USB port. The BBB specs say 100mA is provided, but the modem apparently uses between 230-350mA. I guess I should have used a powered USB hub. Now I guess I'm kind of out of luck. I'm just a bit confused why enough power was supplied by the BBB to power on the modem rather than it being under powered and staying off (like when I try to hook it up to my RPi boards).
I guess you did not read the manual. USB port can deliver 500mA. Sounds like during your power down you corrupted the eMMC.
My suggestion would be to re-flash the eMMC.