I have been having this problem for a while. Games like kerbal space program and arma drop down to 3 or even zero fps if one or more keys are pressed. sometimes this is intermittent. But I dont know how to fix this, so any help is appreciated.
PC specs may help and what keyboard you have
Processor: fx-8350 at 4.2 Ghz
Gpu: Evga gtx 660ti (overclocked)
Mobo: Msi 990fx-GD80
This hasnt happened with any specific keyboard really it has happened on my old razer death stalker and death adder but I recently ( 2 days ago) switched to the microsoft sidewinder and logitech g700. Like I said though this mostly happens in arma and kerbal space program, It is in no way predictible when it will happen. Even after a restart it sometimes does this in games. It may just be a problem with my motherboard, i've had problems in the past with this board.