chopper

Hi all, Just bought the PDR-400IP120 Network DVR + 4 x Mini day/night cameras. http://www.networkwebcams.com/product_info.php?products_id=210 Whenever I setup the Motion Detection Sensitivity the system seems to freeze? I bought a small monitor to view the cameras directly from the system itself but via the remote viwer software I can connect but all the screens are blank and the date/time is reset? It appears to happen after about 10-15 mins, any ideas? A reset will fix it but only for another 10-15mins. Basically, I want all the cameras to record on motion detection 24/7. The HD is upto 85% full but is setup to overwrite. I'd like it to store upto 30 days footage if possible. Any help is appriciated!