Help figuring out what part should I be replacing

The USB data connection on my OnePlus One stopped working.

This means that no connection is even detected on any computer.

This is not a driver issue as the computer doesn't even notice anything has plugged in.

It's not a software/ROM issue because the same applies to fastboot mode and recovery mode - no data connection.

More facts:

1) When plugging to a computer USB port - the battery icon shows the charging (lightning) symbol for a half a second and disappears and it won't charge. The computer, of course, doesn't see a usb device plugged.

2) When connecting to an AC charger - it charges just fine.

3) I already tried replacing the dock connector and flat cable unit - did not solve the issue.

Any insight on this will be greatly appreciated!

Thanks