Trans Problem
 

Ok, for a while now ive had troube with 4th gear, When i shift into it it would pop out i was guessing maybe a keeper? but if you held it there for 10-15 sec itwouldnt pop out until next time you shifted into 4th. well today i was driving and i went to shift into 3rd and the was nothing, it feels like its in gear (at the shifter) but it dont take off. and it wont go into 4th at all, what do you think could be wrong ?