Peugeot Partner y 2005 (gasoline) wont start

[heikkip2rn]

Two years I discovered that the battery had died and after installing new one the engine did not start.
While turning the ignition it sounded like one cylinder only fired and then just starter pulled the engine.
Every attempt was the same. Then some guys just disconnected some kind of pug and then reconnected and
the thing was running again. About a year ago the accelerator pedal sensor died. And car acted just the same.
Now recently car did not start again, bought a brand new accelerator pedal sensor and replaced but nothing.
I checked fuel, fuel is coming through, as soon as battery is connected.
Anybody has some idea what I might check, suspect?