Monitor backlight won't turn off

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https://bbs.archlinux.org – I just reinstalled Arch to get rid of built-up cruft (I've been using Arch for several years now), and I've mostly gotten things all configured the way I want them again. However, when I tell my monitor to turn off (like by putting the computer to sleep, or using `xset dpms force off`), the monitor doesn't actually turn off. Instead I just get a little floating box that says "No DVI-D cable," which is the same thing I get if I have the monitor powered on but the DVI cable unplugged. Previously, the monitor would go to a low-power sleep mode (amber LED, and with the bac (HowTos)