Depends on how your system is set up. the no signal on the TV means that the TV has no signal on whatever Channel or input it's currently set to. Just make sure the cable box is powered on and try changing the inputs on the TV.
Another short cut to boost your wifi signal is to use a "Range Extender". Just plug it in to the wall upstairs and it will boost range upstairs and down.
No signal means press that input button unless you are talking about wifi then move your gateway to a different location
Yes what it means try to reset it
Should call the xfinity store
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