hi, l have a peugeot 206 hdi, when engine is not running the car will change into gears fine but with the engine running it wont change gear, if l start the car in gear it will drive normally in that gear but then l am stuck in that gear!!! any idea is on what it could be!!? any idea is would be appreciated!

NONE of the gears will change if u cannot disengage the clutch plate in motion, from the flywheel in motion.
In other words, if ur release bearing = thrust bearing = throw out bearing is too thin (from age & wear) then it will not push far enough to separate these two spinning discs. TIME for a new clutch.

These three things r always replaced at the same time.
1) the big heavy clutch spring.
2) the thin clutch plate, made of a rough durable synthetic material.
3) the spinning bearing that smoothly pushes on the spring & spins at the same time. It usually makes noise & whines when it gets old. Do u hear this?

Or..if u shorten the clutch cable a bit..OH WAIT, the 206 does not have a clutch cable.you r out of luck on that little trick.

when the car is still, nothing is in motion, then u can shift easily all day long. good luck.