I moved recently, and when I reconnected my ISP weird things started happening on my PC (Windows 7 Home Premium with Service Pack 1). A little background first: During the reconnection, I decided to not run a long wire from my wireless modem in the living room to my PC in the computer room and instead use a wireless USB adapter. I tried out Belkin and Netgear adapters but could not install the software from their CDs (I got errors from both installations). Actually, I made a mistake with the Belkin by eagerly inserting it into a USB port before running its CD, which (I found out immediately afterwards) they warned not to do. Right after inserting it, my PC rebooted! After returning the adapters, I had to run the long wire anyway. When I fired up Chrome, all seemed well, but then:
1. Chrome displays an Invalid Server Certificate page anytime I try to load an https page. I also can't download anything using Chrome or Firefox. Plus, I can't copy any text (after copying I can't paste) nor bookmark any sites in Firefox.
2. I can't run many programs now, with most of them displaying error messages. Some examples:
* IE opens its window, but then after a few seconds it closes.
* AVG Antivirus, Windows Media Player, and Dropbox don't show up at all (when I run them, the busy cursor shows for a few seconds and then disappears).
* iTunes displays an error: "Apple Application Support was not found. Apple Application Support is required to run iTunes. Please uninstall iTunes, then install iTunes again. Error 2 (Windows error 2)".
* Steam displays an "unknown software exception (0x40000015)".
* Microsoft Word Starter 2010 and Excel Starter both display an error box titled "Click-2-Run Virtualization Han..." (can't stretch it to see more) that just says "30015".
* Bastion (a game) and SharpDevelop 4.1 (a development editor) both display the same error: "Please set registry key HKLM\Software\Microsoft\.NETFramework\InstallRoot to point to the .NET Framework install location"
3. Some programs misbehave:
* Spotify's Discover page doesn't show album covers. Covers display fine elsewhere in the program.
* YouTube on Chrome doesn't display comments; they do display on Firefox.
Also, before reconnecting my ISP, I did use my PC a few times; I noticed that AVG wasn't running during those times, but I assumed that that was due to the PC not being connected.
Is my PC infected? I don't see any signs of an infection (other than the above anomalies); there are no popups, no site redirects, and my PC isn't slow. Some of the errors seem to point to a corrupted registry. I explored my System Restore, but I found out that it only keeps about a week of snapshots and I had let more than a week pass before I had even thought about restoring. I've run Windows Defender, which gives me the all clear.
Thanks for any help you can provide.