I have GTX480 Tri SLI (using Koolance water blocks) on an ASUS Maximus Extreme-Z mainboard running a 8000x1440 (bezel corrected) res.
See sig for further components.
GPUs are in PCIe slots 1, 2 and 4.
On startup, 3rd GPU (ie PCIe slot 4) is not recognized in NV Control Panel (fails to load), Windows res settings or in Device manager.
1. Scanned for new hardware in device manager,
2. Scanned for new displays in Windows,
3. Changed DVI cables,
4. Reinstalled NVIDIA display drivers,
5. Reinstalled mainboard chipset drivers,
6. Reseated GPUs,
7. Checked PSU cables,
8. Cleaned dust from all components.
I have connected the extra 4 pin Molex connectors to the mainboard.
I have set primary GPU to PCIe in BIOS.
I have not added any additional hardware.
In BIOS, it shows GPUs in PCIe slots 1 and 2, but shows N/A for slots 3 and 4.
The strange thing is is that when I built this rig last year (July), everything worked without a single issue.
If I reboot after a few hours, everything works again. It seems to progressively take longer between reboots for rig to "fix" itself.