Why do I lost USB connection after disabling HDMI in uEnv.txt?

I’m using BBB RevC, and the kernel version is 3.8.13-bone72. When BBB boot up with eMMC, I disabled HDMI in /boo/uEnv.txt like below:

##Disable HDMI

When I reboot the BBB, I cannot visit BBB through USB connection. The USB connection is lost…

Please tell me how to fix this issue. Thanks a lot.

Sorry, it’s issue from hardware connection. Now it works…