I've been playing Skyrim for something like 40 hours with the graphics on High Quality, everything looking fine. Recently I completed the Waking Nightmare quest, and the textures suddenly look washed out, as though I were playing on Low Quality or something. I can't pinpoint exactly when it happened -- it might have been after I alt+tab'd out after finishing the quest but before leaving Nightcaller Temple, or just after exiting the temple. (I don't know if this is related, but Waking Nightmare also had a bug where I couldn't save during; I found a workaround online, where after the dream sequence I exited the temple, saved, and then came back in, and was able to save normally.)

Anyway, so I tried verifying the game cache on Steam, and it said "1 files failed to validate and will be reacquired"; then when I launched the game, I got the Detecting Video Hardware popup, resulting in "Video settings have been set for High Quality." This doesn't seem to have any effect on the texture quality though. Verifying the cache again results in the same thing; each time I verify I get the "1 files failed to validate", and the Detecting Video Hardware popup on the next launch.

What could this mean?