Hi, i recently bought a Sapphire Radeon HD 4870 512M GDDR5 PCI-E DUAL DVI-I/TVO SKU# 21133-00 S/N 180825044742 flashed with mac firmware. The instructions said to take out my existing card put the sapphire in slot 1, then boot up and install drivers. So i took my Nvidia 7300 GT card out of slot 1 and put in the 4870, then started up. I get the grey start up screen with the apple in low resolution for about 8 sec, then the screen just goes blank. What am i doing wrong?... do i need to keep the Nvidia 7300 GT in slot 2, then boot up connected to that first? Im really frustrated. Could someone please help me? It would be greatly appreciated. Thanks.