I have a GTX 295. Only one CUDA device is detected by the DeviceQuery test program from the SDK… (and by any other…) There is no SLI option in the nvidia control pannel that could be turned on and off, and, anyway, CUDA 2.3 is supposed to deal with SLI now ?
It seems that your GTX295 may be broken or if you have dual pcb card, maybe internal sli bridge is disconnected.
PS:
For cuda calculations you may want to have multi-gpu disabled because in multi-gpu video memory is “unioned” whereas for playing computer games you want usually multi-gpu on to have decent framerate :-)