Upgraded iMac to Sierra OS - no internet now!

[MrsMuddlePluck]

Started off with my printer not connecting to wifi, after dh rebooted everything after ds1s hard drive stopped.

Unable to get printer to reconnect to wifi. After 7 hours of fiddling & 4 online chats to apple support, I was advised to upgrade from el capitan to sierra os. We only bought the thing at Xmas, so the os is already out of date after a month?!

Now I have an iMac that won't connect to wifi either. Thanks apple. They now say I have to backup to an external drive (which I'll need to buy - last time we used one it packed up & we lost all our baby photos, so I'm not keen); wipe the iMac & restore from the external drive.

Seriously? Any tips to avoid this would be gratefully received.

We have been here before with our old imac - upgraded os & mc ended up in the apple store for 3 days, during our busiest time running a business! Apple have form.

[SaucyDough]

What router do you have?