This error is generally caused by not configuring the system correctly to properly support SLI. There are many possible reasons. This article is designed to help you troubleshoot common errors that you might encounter when trying to get your graphics cards to work in SLI mode. If you need help and not sure where to begin, please review the SLI How To Setup user's guide.
1) Your legacy motherboard probably does not have the proper jumper setting enabled to support two graphics cards in SLI mode. Check with your motherboard/PC manufacturer for details on how to enable the correct SLI mode.
2) SLI mode is probably not enabled in the system BIOS (depending on the BIOS, your system may not use the exact term SLI, look for other terminologies such as PCI Express or PCI-e related options). Check with your motherboard/PC vendor to see which BIOS setting(s) you need to set to properly enable SLI.
3) To properly enable SLI with certain legacy motherboards, manufacturer require the reconfiguration of a daughter card to enable the support for dual graphics cards. Check your manual or vendor for setup instructions.
4) Your motherboard may not be providing enough power to the graphics cards. Many motherboards have a 4-pin power connector near the PCI Express x16 slot. This dedicated power for the PCI-express slots preserves the integrity of the power signal. Make sure your motherboard has all the necessary power connectors plugged in.
5) Your SLI connector may not be seated correctly on the graphics cards or its defective. Disconnect and reconnect the connector onto the card again. If you don't have the connector, please contact your PC or motherboard vendor to obtain one. Please note some GeForce 6 series graphics cards do not use the SLI connector.
6) If your graphics card comes with a 6-pin auxiliary power connector, make sure it is connected to your power supply's 6-pin power connector. If your power supply does not have a PCI-express auxiliary connector, please contact your graphics card manufacturer for a HDD to PCI-express power adapter.
7) Your power supply may not be providing adequate power in your system. We recommend a minimum of 450 Watt power supply for basic SLI setup but additional power is needed for a more complex system configuration and higher performing graphics cards. Check here for additional SLI power recommendations. For a list of certified motherboards and power supplies, please visit this link; http://www.geforce.com/hardware
8) Verify your two graphics cards match. For example, a GeForce GTX 670 must be paired with another GeForce GTX 670. Likewise, a GeForce GTX 660 must be paired with another GeForce GTX 660.
9) Verify that Windows Device Manager is showing two identical graphics cards (Example, NVIDIA GeForce GTX 580) under Display Adapters. If not, your graphics card(s) is not installed correctly. Please verify that all the reasons mentioned in this article are resolved.
10) You motherboard may not have an updated system BIOS or chipset drivers. Contact your manufacturer for the latest. For system that has NVIDIA's nForce chipset drivers, you can download the latest driver from our web site, http://www.nvidia.com/content/drivers/drivers.asp
11) Uninstall the NVIDIA display driver and reinstall the driver again. Verify that the OS recognizes the video cards that are installed (check Windows Device Manager). It should show the presence of your two video cards correctly with no errors and conflicts.
12) Your graphics card may not have the latest video BIOS. Check with your vendor and see if a new one is available.
13) It is possible that one of your graphics card is bad. Install your cards individually to make sure they both work.
14) Your motherboard, system or component probably hasn't been certified or support SLI technology. NVIDIA SLI certification ensures a quality user experience by putting each component through a rigorous series of tests including diagnostics, benchmarking, burn in, and card interoperability. Only components that pass NVIDIA SLI certification can be called "NVIDIA SLI Ready." For a list of certified components (power supply, motherboard, CPU, memory), visit the following link; http://www.geforce.com/hardware/technology/sli/supported-gpus
15) Make sure SLI is actually enabled in NVIDIA's Display Properties. Look for the "Set SLI Configuration and PhysX Configuration" or similar panel and enable this option.
16) If you happened to update the latest grapics card drivers and SLI stopped working, before installing the new drivers, make sure you uninstall the previous NVIDIA display drivers from the Windows Control Panel before installing the latest.