I have 3 GTX 280 cards in my system with Win Vista-32 bit edition. I have CUDA 2.1 installed on it. I made a small program to show the number of GPU devices on my computer. The cards are not connected in SLI. They have been placed properly in the PCIe slots too. The command cudaGetDeviceCount returned a value of 1. I have another system with 2 GTX 285 GPU cards. It has CUDA 2.1 and it has Win XP. By using the same command, it recognizes my 2 cards and it returns a value of 2. I need some suggestions on this issue.