can't shift, 99 merc sable

ok... just a girl with no idea what is wrong with my car and no money to fix it!! my car started and shifted into reverse, let me back down the driveway, then when i was in the middle of the road and tried to shift into drive, nothing happened. the gear shift moves through all the different gears, without actually stopping at any of them, but the car doesn't leave park. the transmission fluid is full. recent oil change. don't know what else to check? are there belts involved? something that could have slipped off? if i take the cover off the steering wheel column will i see anything?? please help!!!

watch the shift lever on the transmission while a friend shifts it, it could be the cable's broken.