No Internet Connection

Ok, out of nowhere my internet just stopped working. I have a cable modem and it's worked fine the past six months. I have a PC and iMac in my computer room and the PC works fine when it's hooked up, but when i hook up the cable modem to the mac, it doesn't even detect it. I've tried plugging the cable modem into the mac and then resetting it and it still doesn't even recognize that it's even plugged in. Does anyone have any help? Sorry if i didn't provide enough information about my computer or the modem. Just ask me about it and ill tell you more info.