Drive shaft issue

I have just replaced the clutch on the car. I have fitted everything back together but when putting the car in gear only the passenger drive shaft is engaged. I have taken the other side back out and reseated twice now.
if I put the car in gear but not turn engine on and spin either wheel both wheels turn as they should and both drive shafts are fully engaged, as soon as I actually start the car and select a gear it goes straight back to only the passenger side working,
if I get under the car whilst in first gear and engine running I can freely spin the drive shaft that comes directly out of the gearbox to the drivers wheel in either direction there is no engagement or resistance.