I've got a reliable wifi network but I need good backup facility recommendations please

Running iMac late 2013 and Mac Book Air both running the latest IOS. (High Sierra) I need a reliable back up system. I did have a external hard drive but that seems to have spat the dummy and wont be recognised on either of the two Macs or on a Windows machine. Looking at AirPorts but I don't need the wifi facility. So the questions are:

1. What do you suggest for a back-up set up?

2. Any ideas how I can force the Toshiba external hard drive to be recognised to start again - as in reformat it and can I use it?

Any ideas greatly appreciated