Gearbox problem

I have a Mk 4 Golf GT TDi (2002) Model, the problem I am having is that the car does not move in 1st or 2nd gear, when I put it in 3rd the car moves. Also when I put it in 1st or 2nd it seems really loose like it has not slot in properly.

Can anyone advise me on this, help needed urgently.

Thanks

Yasin