From the recovery console:

del c:\windows\system32\config\system

copy c:\windows\repair\system c:\windows\system32\config\system

That did the trick. My device drivers are mostly uninstalled, and some of my settings were reset (notably, video settings). But this was easily to fix: Windows already had all the drivers, so I just had to go through the motions of clicking through the driver reinstallation.

Now I’ve got class in 10 minutes, followed by lunch, and then three other classes. I don’t feel ready… but I have to go.