I managed to get my hands on a broken 5870 card. The guy who gave it to me told me he was driving his resolution up to much, so the output went black.
I threw it in my linux machine but this card is not being recognized, not even when running "lspci".
But its fan is spinning, it is getting warm over time, and when I pull out the pcie-power-plugs it is beeping like a good card... Also there are no signs of errors while booting, no bios error code beeps, ...
Do you have any ideas what else can I try to get it working again?