Can you give details about your system setup: What GPU, SDK , Driver version?
IMHO, you want to check if there are any OpenCL compliant devices available in your system. You should use clGetPlaformIds API for that.
Also please explain what you want to do by just detecting OpenCL. From C# perpective I guess there is a project that provided bindings for it.
You can possibly look at ICD mechanism. There are some registry entries set for the every platform installed on the system. Just probing the registry values would help.
HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenCL\Vendors might be of help.
OR Check the ICD Extension section in OpenCL extensions PDF.