I dont know what OS or EMU your using, and I cant say Iv ever experienced that issue. I assume its only because you downgraded to win10 instead of staying on 7 or the like.
I know thats useless info, but since no one else has a suggestion ill give u my 2cents.. if my above assumption is wrong and your previous keyboard was ps/2 port or different pc such as a laptop, I don't know how the latest MS OS's handle USB Device Drivers/IRQs, but if you've been switching devices back and forth between usb ports, plugging them into different ports each time... In reality it probably shouldn't matter, but did I mention the latest MS OperatingSystems are garbage? anyway, perhaps that fubar'ed your IRQs or whatnot, there use to be a way to show all current and past hidden device drivers in DeviceManager, so you could uninstall and clear out all/any no longer used device drivers. If microsoft kept this option hidden by default on your OS, u could google how to enable it. If not the option should be present in DeviceManager.
If your able to see all past and present USB devices(this includes the ones not currently plugged in) uninstall All of them, then plug back in only the ones that your using, I would personally also try to keep important devices on there own port, tho that probably shouldn't matter, but did I mention how bullshit latest MS OperatingSystems are?
FYI, modern harddrives are large enough to hold probably every OS combined since the first PC was ever created.. u might as well install/dual-boot an OS that works for games, if u wont games to work properly