After I log on to my Windows 10 machine, keyboard is totally unresponsive (like doesn't work at all) for about 2 minutes.
Mouse works, system is totally responsive, I can run programs (by selecting them with mouse from Start Menu) and they start immediately.
I can open Start Menu with mouse, I cannot open or close Start Menu with keyboard.
After all user part of the boot sequence completes, keyboard is operational again and works normally.
I disabled all user startup programs and defender service (through system policy). It didn't help at all. The keyboard lag has nothing to do with overall boot load (it doesn't work when system seems idle and it doesn't work when the startup programs are starting up). When the lag ends, sometimes I can still see some programs (like Steam) starting, but I can type without problems. High boot load was a serious problem when booting from non-SSD disk, but on SSD the disk queue never fills during normal system operation (no copying, compressing / decompressing large files or large number of small files). Startup programs don't affect system responsiveness in noticeable way when using SSD.
I have very fast SSD. My system boots in less than 10 seconds (full cold reboot). When the Windows (and almost all the tools I use) were installed the problem didn't exist. After I logged in I could use keyboard immediately. Now there's this lag, I have to wait about 2 minutes before I can type anything. I can start a browser, I can open any link, system totally works, but I cannot type any URL, because I just can't type.
I cannot say when the problem first occurred. I ignored it accounting it for one-time lag, but in a month it became more and more annoying.
My keyboard is plugged into USB2.0 port of P7H57D-V EVO motherboard (Asus).
I used Boot Analyzer tool to measure my system boot time. The keyboard was still unresponsive when the tool returned the result.
BTW, there are 2 weird RED USB ports on this motherboard. They don't work, they never did. There are 2 white (USB 2.0, work), 2 red (USB 2.0, don't work), 2 blue (USB 3.0, work, but I don't waste them to connect USB 2.0 devices).
The keyboard is FILCO mechanical.
It doesn't seems like hardware issue at all. First - the keyboard works fine on logon. I can type immediately on logon screen. Then - no new hardware was installed except GTX 960, but I tried to remove all NVIDIA startup programs except the driver itself and it didn't help.
My guess is one of the services run on user logon is blocking either the USB controller (but then why the mouse works?) or Windows keyboard handling.
UPDATE: I checked again with the keyboard connected to PS2 port. Weird, keyboard works shortly after logon, then stops responding, then wait cursor is displayed, then keyboard buffer suddenly flushes executing all requested but ignored shortcuts. So it seems the keyboard works, but all input is buffered until some unknown task finishes, then the buffer is flushed.
Normally when anything slowed my boot sequence I just pressed Ctrl+Shift+Esc to see the system load in Task Manager. When I do it during the lag, it's open when mysterious process is already finished. So I can at least precisely tell when the lag ends. I press Ctrl+Shift+Esc and wait. When the Task Manager appears I can type.