I have had some trouble since I added a wireless connection to my Internet

[Paper Roses]

service. After much--for several days- of, "Cannot find Server", I disconnected the wireless apparatus and now all seems fine.
Of course, I first called Comcast and was told the typical,"it must be your modem". I went to their local office and spoke to a techie who told me how to test the modem. You guessed it, modem is fine.
How would I tell if some neighbor is piggybacking on my wireless network? Does that ever cause a problem?

Now I don't know what to do about my laptop or how to reconnect. I rarely use the laptop so I'm not concerned about that but when my family comes, they want to have the connection available. I don't know what I'm doing...need any advice please.

[Betty88]

1. could you be more specific?

Did you add a new router to an existing cable modem or something like that? If so did you try the good old turn the modem off (unplug), then do the physical connections

Modem-->router-->wired connections like to desktop

Then turn everything on starting first with the modem, then the router, then boot up the wired computer. If that all works then did you set up the router, log into it and do any needed configs like give it a name and set up a password.