sorry no answer, but I have very similar issue. My usb mouse would briefly stop working every ~20 seconds (like a lag spike). Occasionally, both the keyboard and mouse would just completely stop responding. Even after re-plugging the usb devices, I'd get no responce and I'd have to reboot.
This happens for both front panel usb ports and back; I've updated my mobo BIOS and reinstalled the drivers.
OS:Win 7 64-bit
Mobo: MSI Mpower Z77 (Big Bang)