I'm sorry I haven't given details of what I've done so far.
1. I used the DrWeb rescue disk to boot. That found four infected files, which I deleted.
2. I ran unhide.exe to remove the "hidden" attribute that had been applied to many of my files, including everything on the desktop.
3. I installed Avast, did a quick scan and then a full scan.
4. I checked the Windows registry's "Run" section, and found an entry to run a file in C:\ProgramData that had a modification date of 2011/07/15 -- about the time that the problems started. I deleted that registry entry.
5. The file properties for that file said that it was "Tshark". There was another file with a different name that also claimed to be Tshark. I deleted both of those files, even though they didn't come up as positive under virus scanning. (I'm a bit worried that I don't see them in the recycle bin now.)
I'm not having any problems that I'm aware of now, and I can log in to my computer like I used to, but I'm hoping these logs can confirm or deny the state of my system.
Thanks.
Download link:
http://www.mediafire.com/?q9aei19nifj8es3