6 speed rwd wont go into 3rd and 4th?

Hi there
I have an 05 135/350 RWD 6 speed van. The clutch pedal sometimes sticks down and recently this happened when my wife was driving it. She tried in vain to force the thing into gear and since then it wont go into 3rd or 4th gears,it just makes a crunching sound when trying, although all the others are ok. Ant ideas welcome
Rgds
David