General Appeal to Computer Literate People

Ok, here's what's going on.  I thought I fixed the WiFi problems, but apparently that wasn't the whole issue.  Before we spend a minimum of $100 bringing strange geeks into the house, we agreed to poll our friends.  Here is the whole sordid chain of events for diagnostic purposes.

• There are three Internet capable devices in the household, my old MacBook laptop running an outdated Mac OS X (10.5.8), Dave's new(ish) LG gaming desktop running Windows 7, and his Kindle Fire. 
• WiFi is provided by Comcast Xfinity via a cable SMCD3GNV modem/router, or whatever it is. Everything used to connect to this network beautifully.
• WiFi started to get really spotty and unreliable about a month or two ago.  We weren't sure whether it was just crappy service from Comcast or a hacker in our network.  One fateful afternoon last week I decided I would take precautions against the hacker scenario. 
• I went online to log into our wireless router network settings, planning on just changing the network password.  I pulled out the nifty set-up card with all the usernames and passwords we had established three years ago when we first established the network.  The portal would not accept them.  I tried multiple different times.  I verified that my caps lock was not on.  No dice.
• Unable to even log into the portal, much less access the network settings, I reset the router to its factory settings.  Then I rebuilt the network with a new name, new login info, new passwords.  My MacBook logged into the new network without a problem.  
• The LG desktop could see the new network and ostensibly log into the new network, but it insisted there was no Internet access available on that network, or that the signal was very weak.  The problem only grew worse as I went back and forth trying to troubleshoot it, and eventually the MacBook agreed that the network was locked up and would only function via ethernet cable.
• The router was rebooted several times.  No better result.  It seemed to function perfectly well and was unaware of the problem.  All the right lights seemed to be blinking.
• And, yes, we made certain our Comcast bill was in fact paid at the time.
• Eventually, the LG desktop spit out an error message informing me that there was an IP address conflict, which was probably what was locking up the network.  
• After an hour of research, I thought I'd found a solution to the problem.  I connected the LG desktop to the network via ethernet cable, went into Command Prompt and ran IPCONFIG/RELEASE and IPCONFIG/RENEW.  
• After that, all problems seemed to be solved.  Both computers were happily using the WiFi as if nothing had ever happened.  
• Later that same evening, the LG desktop began to have trouble again, recognizing only a weak signal, and then no access at all.  It is aware of the network, but claims the network is not connected to the Internet and that the problem is with the router.  The router is humming along providing wireless service to my MacBook and the Kindle without any trouble.  We don't know what to do about it anymore.

Any thoughts?  Anyone?

Also, does anyone have any glowing reviews or horror stories about Geekatoo?  We'll probably try them before the Geek Squad if nothing else works.