Cable modem connection to a switch

Recently the company that I am working for contracted a job to distribute the broadband connection to the rest of the computers on the network. The broadband came with a Scientific Atlanta cable modem/Gateway device and has four Ethernet ports on it. When ever you connect using a straight through cable it works fine after it receives an ip from the device, then I have connected a switch (D-Link) in a straight mode to the device and connected the computers to the switch. But nothing seems to work. Please Help needed.