NT loses IP address

We’re running NT4 and DHCP connected to a cable modem as our internet hub for a small LAN. The server loses its IP address numerous times during the week. Running IPCONFIG will NOT renew the address. Only rebooting and re-logging in seems to work. Does anyone have a fix for this or a small batch file that could be run from a workstation that would cause the server to reboot and log itself in?
thanks,