The history of this is that I got a conficker/Kido/etc worm in July or so from an infected USB stick and removed it using the Kapersky tool. It seemed to be gone. Since I knew that the worm modifies the registry, I ran CCleaner after removing it, and I have a hunch that's where the problem started - maybe CCleaner accidentally got rid of something that was actually a necessary component of windows?.... though I did back up my registry before running it, and restored it once I started having these problems, to no avail, so it may be something else.
Since this whole escapade, my computer:
1) fails to install most (but not all) updates. the ones that succeed are pretty much only definition updates for windows defender. it doesn't work to install them manually, and i did try to install the update that lets you install updates, but it said that it was already at the most recent version.
2) periodically goes into blue screen of death (IRQ not less or equal) when shutting down. it counts down for a while, then reboots itself. after this, i can shut down from the login screen with no problem.
I'm copying below the problem reports and solutions information, and attaching a zip with some of the files that it identifies. The other three are each bigger than 500MB zipped, so hopefully they're not necessary!
Thanks in advance for your help in figuring this out!
Windows Modules Installer
Problem Event Name: WindowsWcpOtherFailure3
OS Version: 6.0.6001.2.1.0.256.6
Locale ID: 2057
Files that help describe the problem