Sorry for the delay in replying. (I've been working 14 and 15 hour shifts with just a single quick coffee break in each one, followed by 17 hours sleeping to recover!).
Simply installing the latest driver for your video card
might do the trick. (It was only issued yesterday!). You can download it here:
http://www.nvidia.co.uk/content/DriverDownload-March2009/confirmation.php?url=/Windows/375.63/375.63-desktop-win10-64bit-international-whql.exe&lang=uk&type=GeForce
(Remember to restart your PC after installing it).
If that doesn't work you'll probably need to install whichever program placed opencl.dll onto your computer. It's likely to be a gaming program; you might be able to identify it by searching for 'opencl.dll' to see if there's a folder which has a duff version of that file in it - otherwise some trial and error could be called for.
It's also possible to find opencl.dll on the web, simply by googling for that file name, and then installing it directly onto your PC. However my worry about doing so is that there are some dodgy sites out there which might also put something nasty onto your computer at the same time.