I have 2 GTX 275's. After installing the nvidia driver straight from the site (first the CUDA dev. driver, then the 'regular' driver), I rebooted and got the "No screens" B.S. (using BT-4R2).
I've been trying off and on for a week, trying "fix-vesa", "nvidia-xconfig", adding new sources and all that, but none of it worked.
This works for both the 'Primary display device is not PCI' and the 'No screens detected' error (for me, at least, on a couple of machines).
Go through your Xorg.0.log file until you come upon something like this:
(!!) More than one possible primary device found
(--) PCI: (0@3:0:0) nVidia Corporation GT200b [GeForce GTX 275] rev 161, Mem @ blah blah blah
(--) PCI: (0@4:0:0) nVidia Corporation GT200b [GeForce GTX 275] rev 161, Mem @ blah blah blah
TAKE NOTE OF THE CARD YOUR MAIN MONITOR IS PLUGGED INTO - Mine is PCI: (0@3:0:0) or PCI:3:0:0
The easiest way to do the next part is to get the original xorg.conf file created by nvidia-xconfig. If you can't find that, you can restore your pre-nvidia file (rename xorg.conf.backup xorg.conf) and then run nvidia-xconfig to create one.
Anyway, open your xorg.conf file and find this part:
VendorName "NVIDIA Corporation"
and add this line right underneath (or really anywhere in there):
BusID "PCI:3:0:0" (remember, the numbers following "PCI: will depend on your machine)
That's it. Save the file and type "startx". Should start right up.
I'm a linux n00b, btw, but I figured I'd post this just in case - I know I haven't seen any fix like this posted anywhere... Please let me know if this works for anyone else.