I get reverse gear but no forward gears on my auto gear box.after playing about with the gear stick it will go into drive

the drive shaft just drives a pinion gear in the prop box that drives to gears that spin in opposite directions all the time
by selecting forward with the selector rod , a dog gear is moved forward to mesh with one gear that is turning or moves the other way to engage the other gear that is turning
that is the forward or reverse action for the prop
if you have forward but no reverse the it is not a drive shaft problem but a selector rod adjustment that is not moving the dog far enough to engage the running gear

redux. (A/T trans answer not STICK SHIFTED manuals)
no years stated
no transmission stated, auto or stick.

stuck in Reverse.
linkage checks are first.

the trans has lever on the side
called the Manual valve.
it that lever does not go to DRIVE,
then there will be no drive.
there is a cable from the Shift selector to that
transmission side lever.

inspect these parts for proper movement
no damage, not slipping cable, etc.
only you can do that.
or your mechanic.

get it serviced?
check fuses.
check levels in the box.
get box serviced (gear box) manual stick or auto,not stated, by you.
scan it yet, the PCM will tell you trans errors. if they are happening..

The shift linkage may need rebuilding. Inspect it. Jetta 3 2 0L 8V 9

It sounds like you have the Auto box and in it you have 2 bands 1 is the forward and the other one is the Reverse ,so if your forward gears are working ok then the fluids ok so its either the reverse Pump or the Band which drives the reverse gear is worn or buggered .
So your answer is to go to the AUTO MATIC shop and get them to check it out{ IT MIGHT BE THEY CAN ADJUST IT IN TIME IF NOT TO BAD}. AND THAT WILL SAVE YOU A LOT OF MONEY.
Ron

if you have an automatic gear box , then it is very possible that you have reverse band is broken inside gear box , , light will come on because switch for reverse lights may be actuated by shift lever not gears .

there is a foward band and reverse band in auto gerabox's so if you are able to drive forward this gearbox will need to be repaired or replaced .

if manual gearbox , you may find a reverse linkage loose , or gears dammaged in gear box .
good luck hope this helps

u will have to tighen the gear shifter 1st

Auto or manual,,, if auto it could be linkage or the locking button on lever,, or the reverse band has either broken or worn out
If manual box then its either a burred or worn revers gear,, or Selector shaft ball and spring jamed up but only in a 4speed forward gear box or the reverse gear fork pin has come adrift.

manual or auto?? if auto check the oil level with engine running and in gear,wheel chocked up with blocks

check if it has any oil in he gear box.