LaserJet M454dw won't connect

[dbronzan]

Re: LaserJet Pro M454dw, purchased 2 years ago, used in home ... everything working fine until 2 wks ago - briefly lost network connection at home (Xfinity) and when network was restored, printer no longer worked (had previously connected to both a desktop computer and a laptop wirelessly) - kept saying "offline";  as a simple, non-techie user, I tried all I knew to do --but to no avail; had a deadline for a printing need (volunteer work for local non-profit) so took to local computer service shop - they were unable to figure out the problem, but as a "get it up and running to meet this deadline" they connected printer to my laptop via USB - it works!  Still cannot connect wirelessly - AND cannot connect to desktop, no way, no how! Not even via CAT5 cable !! Computer cannot "find" printer.

Have done the turn on/turn off/restart modem routines many times (ad nauseum) - have followed all of the HP SMART directions, still no connection; have tried new CAT 5, using different ports, etc - no connection; modem seems to be working for all other purposes.

My non-techie thinking is that perhaps when the network connection was initially lost, then came back on -- maybe something in the printer that is related to internet connection was "fried" ?? Possible?  and if so, is that fixable? The HP website says there is no service available in my area (Central California)!!   I am beyond frustrated thinking that a 2-yr old printer might have to be replaced.

Oh, and the stuff about "5 Ghz" and "2.4 Ghz" and switching from one to the other - all FOREIGN to me; if that's my issue and someone can explain in plain "housewife" language, I'd appreciate it.  Is this something I need to approach Xfinity about?

Appreciate suggestions greatly - can't afford another trip to the fix-it shop -