The coaxial outlet I want to plug my modem into doesn't work

Apartments/townhouse developments can be really unique.  They may have a contract with Xfinity to manage cable infrastructure, so contact your building management company/landlord first.  That can save you the tech visit cost if there is a current agreement.  

See who is responsible for wiring first.  

Thanks for reaching out, melkonian718! It sounds like your apartment only has 1 working outlet. What you could do is have your modem plugged in there and get some xFi pods (as seen here https://www.xfinity.com/learn/internet-service/wifi/xfi-pod) for the other areas of your house where you'd use internet regular. You could also get a long coax cable and have it reach from the active coax outlet to an area of the apartment you'd like the modem. The 3rd option would be to get an install teach to come out and make the dead outlet active. However, that can get pricey. 

You might be able to do it yourself too in a minute or two with a pair of pliers.  It could be as simple as unplugging your active jack, and plugging in the other one in an equipment/utility closet somewhere if the coax is there just dangling and not connected to anything,  ​but there is no standard for cable wiring.  The cable may come together in your unit, or somewhere else.  Some of it can date back to the 70's, and might even run to the roof for an old over-the-air antenna.

Actually being able to trace the wiring down in an apartment can be a problem too, depending on your situation.   It's why I'd suggest asking building management/landlord about it.  They might know how it's hooked up too if you are unable to determine that yourself.     ​

I only have one coaxial cable outlet in my house. I don’t know how to tell if it’s active or if it’s my modem. I really don’t want to have to pay for someone to do anything I can just do myself. 

@user_i30nzi 

Please create a new topic of your own here on this board detailing your issue. Thanks. The original poster has not returned. 3-month-old dead thread is now being closed.

For future reference, it is better to submit your own post as it creates a ticket to get help, and posting on someone else's older thread can delay getting help.