Rep Power: 0

when the car is off the gears work and when i start the car it wont shift into gears at all,my car is a 91 honda prelude(manual shift)

 
Rep Power: 0

Most likely the clutch master cylinder and/or slave cylinder has went out. It's a good rule of thumb to replace both at the same time to save frustration later on. A hydraulic clutch system works on the same principle as your brake system. Its very important that after replacing the slave and master cylinder that you properly bleed all air from the hydraulic lines to ensure proper clutch pressure.