Get some carb cleaner and blast it into the lock, or WD40 if that's all you have. The lock might be broken but it's probably just frozen or stuck.
This is what a eurolock barrel looks like. The black tab in the middle is what rotates and opens the lock, it pushes the bolt back and forth. The barrel is held in by a screw which goes into the hole under the tab. The screw is on the edge of the door so you can't get to it with the door closed.
You'll notice that the key in the picture is straight, yet the tab is to the side slightly? To get the barrel out you need to remove the screw 'and' turn the key so that the tab is inside the body of the barrel. Then it just slips out.
Bottom line is that if you cannot rotate the key in the lock there is no way to retract the bolt or dismantle the lock. If you cannot free the lock what you will have to do is drill out the part where the key goes. You will then be able to turn the tab with a screwdriver or bent wire and pull the bolt back.
It's possible that the bolt is stuck but it's very unlikely, it's usually the barrel.
Don't worry about destroying the barrel as they are a standard size (although you get different lengths) and are wildly available from hardware stores and DIY outlets like B&Q.