beablebone black is enumerated as ttyACM0 over usb power cable

[pointers...@gmail.com]

My setup :

Ubuntu 14.04 LTS dual boot with windows 7.


uname -a


Linux nikhil 4.2.0-42-generic #49~14.04.1-Ubuntu SMP Wed Jun 29 20:22:11 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

I have a beaglebone black board, connected via a usb cable to power it up, one usb to uart cable. 
Few days back I was able to see the usb to uart as /ttyUSB0, now it is not enumerated.
I checked serial header on beaglebone and it was having 3.3 volts. I checked the supply from usb to uart cable and it is 5 volts
 (However I am not connecting the red cable). 
How can I know what have gone bad? Should I buy a new usb to uart cable?