I know how Jack feels, from the other side. I get calls from local folks who "just can't" get their wifi to work. I go round there with a spare modem/router (an old Netgear that's been all over the place with me), a Cat5 cable, and my iPad.
I put the Netgear next to their modem/router, just to show theirs that I mean business. Then I "sniff" the wifi using WiFiFoFum on my iPad. That usually reveals three or four wifi stations round about, mostly on the same channel.
Then I go to their (wired) PC or connect their laptop with the Cat5 cable, access the router, change the SSID to something they'll recognise, and move it to a channel where there's nothing else nearby. I set a WPA2 (or best available) password that's something they'll remember, with a number on the end.
Then I connect their wireless device to that, have a cup of coffee, and go home. Elapsed time between 30 and 45 minutes depending on how hot the coffee is.
I've never yet had to lend them my old Netgear, and never (yet) failed to get it working.
It's a logical sequence of things to do - if you don't understand, get someone who does to talk you through it. You do need to know enough to access the relevant bits of the router: it's not very likely to work "out of the box".