disapearing network printers

I am new to networks and I have a problem that is beyond me. On the w2kServer, I have installed 2 network pinters (An Oki 5100 and a Kyocera something) on the server several times. Every time, they work from all 7 of the workstations for a while, then mysteriously they disapear (This SEEMS to be happening at around 3:00 pm-or atleast for the last 3 days this is the case) I reset the server and check if they are back . no I fiddle around blindly but doNOT reinstall them, I reset the server again after i’ve actually done no good and viola! they are back again.???????????
Anyone got any ideas?