The output just suddenly failed?
You reinstalled the flash memory in Line 6 Monkey and you still get no output?
Do you get any signal through any outputs when the POD is not connected to the computer?
I'm asking because there is a USB monitor slider level control in the Line 6 Audio MIDI Devices Control Panel I believe in the Inputs & Recording tab.
If that is turned down you'll get no output when connected to the computer via USB.