Q: Peripherals seem to interfere with internet connection.

I was doing some research on the internet this morning. and went to a forum I sometimes visit. As I was typing, I clicked on a bookmark to look up something else, and suddenly I could not get to any websites at all. I figured that the internet had gone down, as often happens. The computer seemed to be connected to the local network, but not the internet. Clicking the Airport connection icon in the menubar, I saw that the computer now was "looking for networks." Then it asked me for the password for the usual network (a password it had previously saved -- I had just minutes before that been connected). I typed it in and was greeted, alternately, with these two messages (paraphrased, because I didn't take a screen shot and now cannot reproduce the behaviour):

"Connection to xxxxxx has timed out"

and

"Incorrect password" [it was NOT incorrect]

also, once, something like "your network configuration has changed"

There was no problem (other than the usual slowness) with the network itself (the other computer here -- sitting right beside mine -- worked fine). This went on for an hour and a half, when I decided to do a permissions repair, restart, etc., so I disconnected the external hard drive and the flash drive. Immediately all the open Safari and Firefox windows connected to their intended destinations.

One at a time I re-connected the two external units and lost connectivity again when I connected the hard drive. But why? Most times that I'm online, I have that drive plugged in and have had no trouble at all. I can't figure out how its presence would make the network settings go bananas.

So now it seemed that I could work online, but had to have that drive disconnected. Not a good long term solution.

Things were working well for a while (other than having to leave the external drive out of service), but minutes ago things froze up again. In order to take the computer into another room, I disconnected my mouse and power supply. Once again, and almost immediately, there was no problem at all connecting with any site. SOME of this could be coincidental -- the intermittent internet connection disconnecting (or reconnecting) just as I pull (or replace) the plug on the peripherals (in particular this nonsense with the mouse and power supply). But surely not ALL of it.

This is too weird.

Thanks in advance for any ideas.

Leonard

p.s.: I should mention that this computer frequently forgets my settings, including passwords, so I wonder if there is something deeper wrong that's less like a magic spell that has been cast on it. It's a 2012 MacBook Pro (9.2) running Mountain Lion.