My 1991 Cadillac Brougham will start up fine, but when you hit the gas it will not catch any speed. I can press gas pedal all the way floor but it wont gain speed. The car has been sitting for a while but it is in good condition.
Sounds like the transmission decided to go on strike. I would start with double checking the transmission fluid level. If it is low, the vehicle may not shift.
If you drop the shifter into reverse or Low (possibly labled as second or first on the shifter) does it move? If so, its possible the the shift linkage may need to be adjusted or replaced. A technician could put the vehicle up on a lift and manually shift the transmission into gear at the transmission itself to see if there is any change in how the vehicle reacts when it should be in gear.