A few weeks ago I exchanged one of my graphic cards because the one, that came with the Mac was broken. For about 3 weeks everything was fine and since yesterday the Macpro does not recognised one of them, although they are exactly the same card. I also swapped the PCI Slots but no success. The MacPro is an early 2008 Model , both cards are ATI Radeon HD 2600 XT. Beside the Radeon cards there are one Fire Wire Card and one UAD 2- Quad installed. One of the cards is recognised as this: ATI Radeon HD 2600 XT: Chipset Model: ATI Radeon HD 2600 Type: GPU Bus: PCIe Slot: Slot-2 PCIe Lane Width: x16 VRAM (Total): 256 MB Vendor: ATI (0x1002) Device ID: 0x9588 Revision ID: 0x0000 ROM Revision: 113-B1480A-252 EFI Driver Version: 01.00.252 Displays: DELL SE198WFP: Resolution: 1440 x 900 @ 60 Hz Pixel Depth: 32-Bit Color (ARGB8888) Display Serial Number: 7373185SLTDM? Main Display: Yes Mirror: Off Online: Yes Rotation: Supported DELL SE198WFP: Resolution: 1440 x 900 @ 60 Hz Pixel Depth: 32-Bit Color (ARGB8888) Display Serial Number: GM778857221M Mirror: Off Online: Yes Rotation: Supported and the other one as this: Display: Type: GPU Bus: PCIe Slot: Slot-4 PCIe Lane Width: x4 Vendor: ATI (0x1002) Device ID: 0x9580 Revision ID: 0x0000 Kernel Extension Info: No Kext Loaded any idea someone? Thanks!