cant get into gear with engine running

[passat_brum]

Hi Guys/gals
I have a 2004 1.9tdi 90k, replaced the cam belt and the 2 other belts all with tensioners etc.
With the engine running I cannot select a gear, when engine is off it goes into gear.
I have bled the slave cylinder
put it into gear with the engine off then started...doesn't move forward until clutch operated.
The only other work ive done is to change the gearbox oil, using the correct spec.
Does anyone have any ideas?
From what I have read, if it was the slave cylinder -not disengaging the clutch it should jump forward if in gear then started??
tia