History: A few months ago I replaced my Mac Pro's default video card with a GTX 570. This card works fine with OSX, but unfortunately it isnt officially supported, so any time I hold option when booting, it wont display anything (screen remains black). I got around this by simply altering the default startup disk whenever I wanted to boot into windows. Once in windows I could change the startup disk from the bootcamp menu in the toolbar to boot back into OSX. Yesterday I attempted to boot into windows, but my mac pro wouldnt display anything. After 10 minutes or so, I shut it down, and tried again to no avail. The problem is that normally if an issue occurs I can just reset the p ram in order to boot back into OSX as normal. This didnt seem to have any effect. Still a black screen. Then I tried swapping out the GTX 570 for the original video card it came with. This would normally solve any issue of this sort, but still nothing is displayed. At a loss here. Any ideas?