One computer can't access wifi?

[Richard]

Unfortunately, some computer wireless adapters are not compatible with some routers. I had a similar problem with my old laptop when I installed a new router. Last week I uninstalled the drivers for the wireless adapter in the laptop and then reinstalled them. This fixed my problem.

I don't know whether you can do the same sort of thing with a Mac.

If the Mac will work with a USB WiFi dongle, you might try that as an alternative to using the Mac's normal WiFi adapter.

I hope this helps.