Hi,
Just had the same problem this morning. Both the keyboard and mouse were not working anymore at login screen (no problem at bios level where both are working). This is a new PC bought 3 days ago. Worked like a charm until this morning. No new installation since a few reboot yesterday without any problem. So I can't link the problem to anything installed recently....
No way to start the PC in safe mode and even a PS2 mouse was not working (except in bios...).
Luckily I had installed teamviewer on the PC and could login and see what's wrong (thanks to Gaz25 who mentioned remote control, as I had forgotten about it and would not have tried...).
I had two USB Controller not working. Only had to disable and re-enable them for both the mouse and the kb to work again.
Intel(R) 6 Series/C600/X79 Series Chipset Family USB Enhanced Host Controller - 1D26
Intel(R) 6 Series/C600/X79 Series Chipset Family USB Enhanced Host Controller - 1D2D
Rebooted and same problem again, but this time only one controller down.... So the problem is NOT fixed, but at least with the help of another computer I can temporally fix the problem until next reboot....
Still working on it and if I get a proper fix, will let you know.
EDIT: Tried what was suggested by Gaz25 to uninstall the two controller drivers and reboot. It worked. Now I need to see with time and multiple reboots if it doesn't happen again. But I will keep for sure teamviewer installed in case ....
EDIT: Did not survived at the 3rd reboot.... but for some reason the PS2 mouse was working (first time) so I could use it to start the virtual keyboard, login and disable-enable the controller to re-enable my mouse and kb again.... So still no proper fix but a better workaround than using another computer with teamviewer...
EDIT: As suggested in the forum below, I have set the USB Legcy mode to "disabled" in the bios and it seems to have fixed my problem. At least after 5 reboots no problem. Let see with time.