Before I state the problem here is a breakdown of the system hardware. Intel x6800 Tuniq Tower w/ Delta fan (up to 150CFM!!!!) Asus P5W64 WS Pro 4x1GB GSkill PC8000 HZ Sapphire X1900XT Crossfire Edition 512MB HIS X1900XTX 512MG Areca 1230 w/ 4xNEW 36gb Raptors 2xOLD 36gb Raptors Soundblaster Xfi Tagan Dual Engine 800W PSU I have installed Windows Professional x64 Edition on a RAID 0 array. All updates, and most recent drivers for all enabled hardware. Catalyst drivers installed are 7.2 and directX9.0c. All is fine until I enable Crossfire. At this point I should point out that the two graphics cards have run in crossfire mode without problem in Windows XP Pro before I had a motherboard change and RAID array failure. Once Crossfire is enabled and you try running any of the Futuremark 3DMarks there is either a directX error or the system hangs with a black screen or you get a BSOD due to one of the ATI dll files. The system freezes if the Catalyst Control Centre when you try to change either 3D or video settings. It there a problem with 64bit systems? As stated the same system ran this fine under XP Pro. Any help appreciated.