I figured I'd follow up on this in case it helps anyone else. I ultimately went down the path of hardware replacement. Dell first replaced the keyboard itself, but that didn't correct the behavior. Next, they replaced the "daughterboard", and that also didn't help. Finally, they replaced the entire system board / motherboard, and that corrected the issue.
I have an m17 R4 laptop, purchased a few months ago. About a week and a half ago a problem began, where the keyboard wasn't working at all. None of the keys worked. Rebooting didn't fix it, system restore didn't work, driver reinstall didn't work. An external keyboard connected to the laptop worked fine. Ultimately I fully reinstalled windows, and it seemed like that fixed it. But within a day or two, the problem had returned. This time, reinstalling windows completely DIDN'T fix it.   [IMAGE]   The symptoms are: Probably the most important thing: Any time the keyboard fails, I will see a failing USB device in the Device Manager, and one of the "HID Keyboard Device" entries will be gone. The failed USB device is called: Unknown USB Device (Device Descriptor Request Failed). Any time that's present here, the keyboard doesn't work. In the few times the keyboard has started working again, this entry will go away, and I'll see the "HID Keyboard Device" again under Keyboards. This is shown in one of the screenshots. The keyboard does work perfectly when in BIOS screens. I went into Diagnostics in the boot options, and I can test all the keys, and they work there. Similarly, I can hit F2 / F12 on startup to enter BIOS settings or Boot Settings. However, once I get to the Alienware logo, and I see the wait spinner appear, that's when the keyboard stops responding. Up until then, I can toggle Caps/NumLock. But once that wait spinner appears, the keyboard is non-functional. After booting into windows, one part of the keyboard works: I can toggle the T-Pad via Fn-F11 (T-Pad) key. That's the only key that works. All of the RGB lighting works. External USB keyboard works fine. I also decided to see if the keyboard worked if I ran Ubuntu off a thumb drive. Short version: The keyboard doesn't work in Ubuntu either. It works while I'm selecting some boot options, but then when it actually loads Ubuntu, I see the USB errors listed here: [IMAGE]   I've spent a long time searching for solutions to "Unknown USB Device (Device Descriptor Request Failed)", hoping to resolve this. But so far there has been no lasting solution. Here are the specific things I've done. With all of these things, I've done them several times so far over the course of the this past week. Reset BIOS settings to defaults, save and restart Flash the Bios. I've tried four different bios revisions from dell's website, trying them one at a time, with no change. Delete entries from Device Manager and rescan for hardware changes, including uninstalling USB Root Hub. On one occasional, as soon as I deleted the USB Root Hub, and rescanned for hardware changes, the keyboard started working again. That hasn't worked on subsequent failures. Fully reinstall Windows with a clean format, using an install media from Microsoft's site (not Dell's recovery media). It's worth mentioning that even when reinstalling windows, the keyboard ALREADY doesn't work on screens like setting up partitions. For example, I can't enter in numbers for the partition sizes. So, just getting out of the BIOS, the keyboard's already dead. Unplugged power supply, help down power button for 30 seconds. System Restore Opened the backpanel, reseated the battery, and reconnected the three cables leading into the Keyboard Controller. (I didn't go any deeper into the laptop than that.) Called Dell several times. We're now at the stage where they just want to replace the motherboard, which is super annoying because I'm outside the US for several months, so there's no practical way to do that. Right now, it feels like there's some random chance that doing a system restore, a clean windows install, or a reboot, can very occasionally get the keyboard working again. Everything will look fine in the device manager, and the keyboard will work perfectly for a day or two. I can reboot and it comes back fine. But then eventually on a reboot, it will break again, and remain stubbornly broken for a long time. Today I've rebooted a dozen times, done driver installs, bios flashes, fully formatted and reinstalled windows, and it's still not coming back. So, I'm hoping someone might have some other ideas on what I might try to resolve this. I've tried everything I can find on any article discussing "Device Descriptor Request Failed", but nothing consistently works, or prevents this from recurring. My vague feeling is that this may be a loose connector in the laptop, but I don't know. Maybe it really is a complete hardware failure, but I'm hoping to find some solution I can do myself. Thanks.
m17 R4, keyboard stops working, Unknown USB Device (Device Descriptor Request 
Failed)