Tough call.
Maybe an Apple store, if you have one nearby, would be first shot. After that, likely a new one as it is almost 5 years old.
I had an old 6 year old Sager running Windows 7 (originally) that puked a week or two ago. Paid $4K for it. Old hardware and the internal modem/Wi-Fi/Lan hardware finally gave up. No connection to anything worked even being cabled. Couldn't even deactivate software either. It went immediately to a "black screen" which means you are toast with Windows.
Maybe 4 years into ownership, the X-rite i1 software told me to "Crank up the brightness." I couldn't as it was max'ed out already after four years. I tore into it and replaced the LCD screen with a $120 LG replacement out of LCD Screens in Seattle, Wa (I think?) and got me back the brightness. But two more years later and the Wi-Fi/Lan pukes and it's a no-go to anywhere. It's dead.
Time for new Apple gear. This stuff doesn't seem to make it with a new OS or drivers made for newer stuff and then it runs iffy with older hardware stuff.
Okay. Even my new wiz-bang $2,500 gaming computer running Windows 10 Home and the latest nVida card pukes too after only one week of ownership.
SG