Plug those keyboards (one at a time) in another PC system. If they do work there then something may be happening with your motherboard or the OS. Try to use the onscreen windows keyboard and check if the m key works. Try to clear the CMOS and check all the available USB settings in the BIOS, enable all USB compatibility settings and try to use only USB 2.0 ports for the keyboards. If nothing works your motherboards is probably damaged and needs replacement. It's rare but it can still happen. Also please post your complete system specs in order to get more accurate advice, especially the motherboard and the keyboards. Good luck.