disconnecting from the network
 

Hi,
I am new to this forum and thought that someone might be able to offer some suggestions to why some of the computer users on my network simply disconnect randomly. There are 57 users on the network, some desktops, but mostly laptops that are all hardwired, all with static IP address assigned and no wireless access. The router is about 5 years old. I noticed this probem about 8 months ago but it was so infreguent that a solution was not urgent because the user could just reboot and the connection was fine again. But now this seems to be affecting more and more of the computers and happening more often. I've noticed the problem mostly on desktop users but it happens with several laptop users as well. I've installed new network adaptors on some of the older computers, but haven't noticed an improvement. The only message the user sees when this happens is the "the network cable is unplugged" but it is not unplugged. Any suggestions would be greatly appreciated?