I spent more than an hour trying to get cable working at the new house this weekend. It’s really not for people who aren’t comfy with getting dirty. And you need to have a good grasp of physical layer troubleshoooting.
If I had it to do over, I would start outside and try to figure out which cable is the one coming from the Cable company. Outside of my house, there was a Verizon FIOS box and an orange cable, which was new looking and capped with a terminator. I took a guess the Orange one was the Comcast XFinity drop since the previous owner had FIOS and the orange cable wasn’t connected to anything.
Step 1 - First… use a long cable and connect your modem directly to the outside drop and make sure it can acquire signal. Consult your Cable Modem user guide for how to read the indicator lights. If you can’t get this working, nothing else will matter.
Step 2 - assuming step 1 passes, try to learn about the cabling inside yourself using a tool like the Klein Tools VDV512-058 Coax Explorer Plus Tester.
Step 3 - Connect the exterior cable to one of your internal cable drops and connect the modem on the far side of the cable drop inside the house.
If your modem indicator lights can’t acquire your cable may have too much signal degradation. You can try other internal drops if any are available.
If your modem indicator lights show that it was able to get signal you’re pretty much good to go to call the cable company and begin the more painful part of being forwarded around and placed on hold and so forth to activate your service and register your Cable Modem.
I don’t recommend this for people who aren’t very technical. Pay the extra money for the install if it makes sense to do so.