errr wasd ftl. arrows with the keyboard sideways, so your thumb is pointing down back at you. thats the way real pros play.
but back on topic, thats not the default crouch button so have you made sure its set to crouch? if it is and not working could try inputting via the console. years since i played cs properly so forgive me if this is wrong but it would be something like
bind \ "+crouch"
type that in console i think binds it to crouch.