System Keeps going off line

Hi to anyone,

I have a Dell PowerEdge 2800 Server with 11 workstations, my problem is that everyday one of the computers goes offline sometime in the front office sometimes in my back office or just anywhere in my office. 3 computers are using Windows 2K professional and the other 8 is using Windows XP Pro. The Server is using Windows Server 2003 standard with 4-80 gig hdds and 1 hotspare.

Can anyone tell me why does this keep happening? Also, sometimes it says limited or no connectivity. Sometimes I have to shut down the system to solve the problem, sometimes it work and sometimes it doesn't.

I need some help in this area. Please email me with your comments.

Thanks,

John