i bought an ATI hd 6870 today and im swapping from nvidia, i installed the hd 6870 and i plugged in the vga to dvi adapter to the card then put my monitor vga into the dvi adapter, then when i run my pc i get no signal on my monitor, ive read forums that say i need to uninstall my nvidia drivers and then install ati drivers but how can i when my pc wont detect the new graphics card