So I was playing a game last night and every one of my peripherals decided to stop working midway through. I rebooted my computer, and my mouse worked, but not my keyboard. After a couple more reboots I was able to get everything working so long as I unplugged just one thing (in this case, my headphones). Once again though, today, I couldn't get my keyboard working until I rebooted several times.
I thought maybe this was an issue with my power supply starting to die, but then I remembered that I also upgraded to 8.1 last night and got to thinking that it might have a problem with the USB ports on my motherboard. It was kind of a bear to set up when I first built the computer (drivers weren't ready for Win8 right away, had to do some weird workarounds to get the USB 3.0 drivers working, etc), but has been fine ever since. And when I rebooted the first time, I went into BIOS to see if I had some setting screwed up, and left it there for about an hour. The mouse and keyboard worked just fine, but the second it went to Windows the keyboard stopped working.
I've got the latest mobo drivers (Gigabyte GA-Z77X), but I'm not sure what else to mess around with at this point.