I have the same problem with my hd300 after i tried to update firmware 2.01 that was not finished succesfully.
Before firmware update anything worked fine. Now the pc just reports unknown device.
I already uninstalled and reinstalled driver and monkey v1.62. I'm not able to install 1.43 as posted in other threads as monkey disappears if i do not agree update.
USB cable and port are ok. I resetted also POD HD300. But nothing helps.