no reverse gear

i have a2000 saturn Ls and the transmission works except for the reverse gear. i changed the tranny fluid and filter and that didnt work. I was told there are 2 bolts that help the car go into reverse that might be worn or broke. then someone said it might be the valve body. Anybody have this problem before? what do you think it is???? i dont want to replace the whole tranny if i dont have have to. HELP!!!!! before i blow the damn thing up!