So, kind of a doozy, let me know if I should post this somewhere else, but here we go:
tl;dr: Can only connect to a few select webpages (fb, bank, gmail, etc.), most others time out immediately (google homepage, ap.net, espn, etc.). Sometimes unable to connect at all or network will disappear completely. Happens at random times on a few select networks that I use semi-regularly.
Long version: I run Windows 7 and Firefox with adblock, Microsoft Security Essentials, checking with Malwarebites anti-malware and ccleaner every so often. Don't know if any of that matters.
There are these two coffeeshops that I go to fairly regularly, and most of the time I have no problem connecting to their internet (like right now). But every once in a while, one of three things happens (pretty much only on these two networks; my apartment and many other networks work pretty much without issue): either the network won't show up at all, it'll show but I'll be unable to connect, or I can connect but only a few sites will load; facebook, my bank and credit card sites, gmail, google maps, google docs for sure, plus a few others that I don't regularly use. Sites like google homepage, ap.net, nytimes, espn, my school website, and more that I don't regularly use will time out immediately, as if I wasn't connected to the network. As far as I know, noone around me connected to the same network is having the same problems.
I've tried clearing browser temp files, troubleshooting network adapter, restarting my computer, checking for virus/malware, most of the things a 22 year old of slightly-above average computer literacy knows to check (I don't know scripts or command prompts besides googling my issue and copy and pasting from there).
Then, sometimes I'll get booted from the network (if I can connect at all), where then I can reconnect immediately and everything works fine. Can anyone tell me what I can do to stop this from happening?
Edit: I've had unrelated problems with this computer in the past, so I'm not ruling out some kind of hardware problem, if that could even cause this. I don't know much.