i have not driven my 1972 4 speed corvette in about 18 mouths. the car reversed out of the garage about 15 feet, but now i can not get her into reverse. all the forward gears shift fine, but she just will not go into reverse.

i'm not a gear head, i wish i was, but i never learned or worked on cars. i'd like to fix this if someone can help w/ what might be the problem. i realize i should not have let the car sit so long, but everything worked fine last time i drove her. thank you for any help!!