The short version of my problem is that at some point after a reboot, certain web pages fail to load. I'm not sure what the root cause is, at all. I am running Windows 7 SP1 and was up to date with updates when this started.
When it started happening:
Thursday night, the power flickered at my apartment and made my computer reboot. I figured it was a good a time as any to install Windows updates since I hadn't done that in a while. After doing so was when I first noticed the problem.
What happens is after I reboot, at first, everything works fine. At some time after, some web sites just don't load. The sites that don't load are consistent (if I reboot and wait, all the same ones fail). A couple examples are bleepingcomputer.com itself and any of Valve's (the game developer) sites. It doesn't seem that computer help/anti-malware sites are all not working, since MBAM and AVG's sites work. Google itself always works and when Googling for info on this problem, I seem to find more sites that don't work than do, once it starts happening.
I don't know specifically at what point stuff stops loading. I tried rebooting then going to read a book for an hour, and it was working when I tried immediately after. If I reboot and open Firefox with a ton of tabs and start browsing around, it might stop within a few minutes.
What I tried:
At first I thought it was my Internet connection or router, but using my phone connected to my own wifi lets me view the pages I can't on my desktop. I don't have any other devices to test besides my phone. So, I don't think it's my router or my ISP.
The same pages will fail to load in different browsers on my desktop. So, it's not specifically Firefox, Chrome, or IE.
I tried using a USB wifi dongle instead of the onboard NIC I usually use, but the problem still happens. So, it's not my NIC failing.
I tried using telnet to manually fetch pages but it also doesn't work (telnet www.somesite.com 80, then entering "GET / HTTP/1.1" and then "Host: www.somesite.com" but it just sits and does nothing; if I do this immediately on reboot it works as expected).
I tried scanning my computer with Adwcleaner, MBAM, and AVG's free scanner, but none found anything interesting. I tried uninstalling the Windows updates in case they were related, but that didn't help. (Although KB2884256 doesn't offer to uninstall itself.)
I have no idea what's up with this. I don't know enough to rule out either malware, a software problem, or a hardware problem. But, nothing finds evidence of malware. I thought maybe the power flicker might have ended up frying my NIC, but the wifi dongle also didn't work. If some other hardware was malfunctioning, I'd think the problems would be a lot less consistent and less specific than only some web pages failing to load. Like, random crashes/blue screens/reboots if it was bad RAM/motherboard/CPU. The only things left I can think to try are a live CD to try scanning for malware again or just reinstalling Windows.
Any ideas on what else I can do to check on the malware angle?