CUDA capable devices are busy or unavailable


I installed CUDA v7.5 on my PC this morning (Window 7, GPU:NVIDIA QUADRO M4000). I ran deviceQuery and I was quite sure that CUDA was installed properly. However, whenever I tried to run CUDA program, the error message:“all CUDA-capable devices are busy or unavailable”. I also restarted my PC and ran my program again but nothing happen. Any suggestion on how to fix this?