Wi-fi problem

I hope one of the experts here can help with this odd problem!

New iMac 27" 3TB Fusion, 32 g Ram.

Connects easily to my Netgear router but ONLY to the Netgear-5G, not to the alternative 'Netgear'. I often lose the ADSL line where I live so have a Vodafone modem as standby, but it won't connect to that either. Nor will it connect to the iPhone hotspot. Everything else (2 x MBPro, 2 x iPad) will connect to everything but I really need this standby to be available.

Can anybody help?

TIA!

Terence

 

FWIW, after talking to Apple Support for some time, it turns out to be a problem with the network card. After only a little persuasion, Apple are replacing the machine at the end of next week. They say it can't be before, since they're making some changes in the iMac... Or are the just getting a refurb ready for me, I wonder... Same specs, anyway, so fingers crossed.