Thank you very much for your replies.
I´m a beginner and this is my first GPU for mining,
I can´t speak for the old owner, but before I posted here, I didn´t mess with the BIOS, I only tried to find a fitting ROM
.
I bought this Card to add it to a Mining Rig of a friend of mine,
I brought him the Card, after a few days he told me that the "Performance BIOS" is broken and he can´t use the GPU like this.
Because of his statement, all I tried was to fix the BIOS and because of my lack of knowledge I didn´t know about the Compute Mode and as batsonxl suggested,
activating the Compute Mode did the trick.
Thank you all very much!