My unstable wireless set-up at home finally collapsed and I went offline last night. I was seriously considering taking all my hardware back to Harvey Norman's and kicking up a big fuss about it, but it was already quite late and I was lazy. So for one last time I carted my desktop back out into the living room to reconfigure my router, calling customer support for any advice they could offer. Helpfully, they suggested switching the power off the cable modem and router before reconnecting both back to my desktop. Nothing I hadn't already done several times before. Duh.
Oddly enough, for once the router configured itself perfectly on my last attempt, the whole process finishing without interruption. Now everything's up and running again, as stable as it ought to be. As usual, no idea what I did right.
If anyone thinks I'm a tech whiz, I tell them the truth: it's just serendipity.
Just realized I didn't have to move my entire desktop outside to configure my router. I have a laptop, don't I? Doh!