Well it came down to it, and I had to replace the laptop's hard drive. Fortunately full backups were already made, and it just took time to do it all. A surprisingly large amount of time: I apparently have one of the few laptop brands that doesn't make the hard drive easily accessible, and I damn near had to take the whole thing apart! Here's the step-by-step video I used to do it. How tiresome. Thanks a heap, Dell.