Windows 10 USB only working if device plugged in during boot

I got a PC with a ASUS B85M-G motherboard and the following problem. None of my USB ports (neither at the back, nor at the front, neither USB 3.0, nor USB 2.0) work. Actually, they don't work for devices plugged in to them after Windows has booted. A device that is already plugged in during boot (mouse, usb-stick, ...) is perfectly detected and usable. When I plug in a device at runtime and then reboot Windows, the device is available.
Sometimes (but not always), a Windows alert message saying "USB device not detected" or the like is shown. When that happens, there's also a unknown device called "USB-STICK" in the device manager.
My device manager's usb-section looks like this: https://anchr.io/#/image/OdjZd.png. The usb-related BIOS settings look like this: https://anchr.io/#/image/v0Q2g.jpg. In forums I found that my problem could have something to do with the xHCI mode, but neither disabling nor enabling it helps. Any ideas?