The cell is only "blocked" by the bars on the dungeon side. When you throw the switch, it opens the back gate, which leads to Mordred's underground lab.
(see related question)
i do not know what you are talking about
There are many doors on Astro Knights island, but none appear to be blocked. The gate to the dungeon cell is opened with the switch when you enter through the library. The underground lab is opened with the small key (from under the village fountain). The dirt wall is easily knocked down to access the back of the dungeon cell. Later in the game, the Golden Key must be drawn and the cards must be turned to open the entrance to Mordred's castle. (see related questions)
it is in the dungen cell.
you can not
Merlin the mechanical owl will recover the fuel cell for you. Feed him a robot mouse and he will retrieve the dropped fuel cell : point to him, then to it.
You have to feed him the mouse. Merlin the owl will follow you into the passage to the dungeon cell, and you can click on him and then the fuel rod and he will get it for you.
give him the robot mouse from the cell
The wall between Mordred's lab and the tunnel to the dungeon is dirt. Push hard on it. The cell in the dungeon is accessble from the underground lab built by Mordred. You should feed the mouse from the castle to the robot owl, who will then follow you and retrieve items for you.
There is no way into the cell from the library. Throwing the switch opens the "back gate" to the cell, which you can access from Mordred's underground laboratory. (see related question)
The key in the dungeon doesn't work. You throw the switch and come into the cell from the back way. (see the related question)
Feed the mouse to Merlin, the mechanical owl, and he will follow you into the cell. Click Merlin, then the vial, and he will retrieve the fuel rod for you.
In the dungeon under the castle library, pick up the cheese and pull the switch that opens the back gate of the cell. In Mordred's underground lab, once you feed the mouse to the owl, you can go down the passageway to the cell gate. Next to the bars, the wall is dirt and you can just push it down.