Change another cable (CAT 5 UTP cable or higher standard, say, CAT 6) if you can not make it work;
besides that, check the cable you used is direct cable instead of cross cable(your WAN point should use direct cable connect to cable modem)
How to check? see the sequence of the colors at the two ends of the cable,(normally it is [white Orange],[white Blue][white Green]][white Brown]), if they are the same, it is direct cable, if one side is like that, the other side the orage and green color are shifted, it is cross cable, otherwise it is nothing....
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