Re: Just got HDMI Cable in.... TV not taking signal from it
According to Hitachi your HDTV has HDCP, so that shouldn't be an issue. I'm using HDMI on an 8300HD with no problems so unless Cox hasn't enabled the HDMI port on your STB it shouldn't be a problem either.
You can try rebooting the 8300HD. Just hold down the power button on the box until "boot" appears on the led display.
If that doesn't fix it you'll have to try another HDMI cable or give Cox a call.
"You know the difference between cannibals and liberals? Cannibals only eat their enemies."