Stan - the hard drive is mounted on the bottom panel of the NVR. You'll need to open that panel and disconnect the hard drive cables. There should be a single connector with both data and power molded into one plug. Disconnect that from the drive and then try to start the NVR normally. If it won't start with the hard drive disconnected, there is only one other option. There is a reset button on the back of the unit. You want to power the NVR on, and then press that reset button for 15 seconds. This will lose any setup you have done as well as remove any users and passwords you have set up. The network will default to 192.168.0.120 too. If it comes back up after the reset - the user will be admin and the password will be admin. Then power the NVR down and reattach the hard drive to see if it will still start up with the drive attached. If it fails to start after that, the hard drive may be defective, and causing problems the NVR can't overcome. 

Let us know what you find.