HP printers

We have two hp 4350 laserjet printers, both are connected to the network through jet directs. For the past week or so we have had a problem with them not printing. During the time when they won’t print, i can ping them, and telnet, but cannot hit the webadmin interface. This will last for about an hour, bith alway stop working at the same time. I have snffed network traffic and dont see anything unusual.