Recently bought a Nehalem mac pro for business and (gaming) pleasure. The Mac video card is the standard GT 120. Installed Vista 64 via Boot Camp and installed my old PC 8800 GT in the other 16x slot. Everything worked fine in both OS X and Vista - the mac using the GT 120 and Vista using the 8800 GT. Then I ordered a GTX 260 to replace the 8800 GT. Already had the two 6 pin motherboard power leads required to fuel the GTX 260. The problem is that the Mac won't boot now into either OS X or Vista. The startup chime is audible, but then nothing. It's not a fault with the GTX 260 as when I removed the GT 120, it booted into Vista without a hitch. I can't figure out why the Mac won't boot at all when both cards are connected. Tried installing them into different slots too. Does anyone else have this configuration (or anything similar) and has got it working? Could it be that the GTX 260 combined with the GT 120 draws too much power when both installed? Taking out the GT 120 each time to play games is not an option!