AMD HD5450 not working under Optiplex 980

Hi,

I am using a Optiplex 980 Low Profile for my Homeserver. I wanted to upgrade with a AMD HD 5450 Low Profile.

That was not working. The BIOS says "Alert! An error occurred initialising PCI Slot 1" (or something like this).

I updated my BIOS from A16 to A18. I reset the BiOS. I checked all BIOS Settings.

I tested a NVIDIA Quadro 410. Yea... That was actually working. But the Quadro isn't mine and just borrowed. 

That's why I am here. Maybe does anyone know how to got the AMD working? What iam doing wrong? Is this Graphics Card maybe unsupported?

Please help Me, I am out of Ideas.

Thanks,

Robin 

PS: The AMD is working under some HP Computer at my work perfectly fine. GPU-Z says also all good.