I need help! Strange keyboard input lag when launching games.

Basically, whenever I open certain games like Gmod (or half the other source games including source mods from 2009), Starpoint Gemini 2, Outland, FNaF, this wierd shit happens where all inputs from my keyboard will wait ~10 seconds before 'pressing' the each key, then hold the key down for ~5. It is also permanent until restart/shutdown. Changing zoom level and resolution of the system also has this effect. Gmod is arguably the largest game I have, so it would be a damn shame to lose it, and half the games I will purchase.