Probably it's fixed by now. But still: If you have an active warranty / support: call HP to reset it for you. If not, you should connect the USB cable, install the driver if needed and connect to the virtual com-port with something like putty or any other terminal software. It will show among some other info the serial number of the unit.
First try the defaut username / password: Admin / !admin, or manage / !manage
If that doesn't work, try with either username restoredefaults or restoreusers, with the serial number as password.