Windows Server 2003 Disconnects at least 3x daily

We have a network server that has about 30 users, just recently it starts to disconnect users from the network (ie. people cannot access the drives and the files that are shared from the server). I tried restarting DHCP but the option under All task is disabled. When I go to the users computer and check ipconfig it gives me the correct specs, same as with the server.

Any ideas?