Mobo Asus M2N-E-SLI with 4Gb Memory.
I just switched from a Geforce 8800gt to a Radeon HD5670. I pretty much thought it would be case of unistalling the Nvidia Drivers and turning the PC off and swapping the Cards over in the PCI-E slot and booting up and then installing the drivers for the new card. There is no power connections needed for the new card.
However the pc will just not boot up with the new card. I just hear/see the dvd drives spinning up, but the monitor light remains orange and never goes green. I've had to put the old card back in just now.