Hello Koepel,
Thanks!
My answers below:
Is it an official Arduino board ? - Yes
Can you give a link to where you bought it ? - It was part of a toy, called " KOSMOS 620523 Easy Elektro - Coding." - The link points to their website: https://www.kosmos.de/experimentierkaesten/physik-elektronik/10328/easy-elektro-coding
Which Operating System do you use ? - Windows 8.1
Where you able to upload a sketch before to the board or did it never work ? - Yes, it has worked before