KdenLive: Nothing is being rendered on Windows?
I was having the same problem. Found this fix from the bug reports.  I did it all, exactly as it says, including the part that changes the melt directory in the program as opposed to moving the melt file to match the directory, and it worked. I did not lose my saved project that previously wouldn't render. It's saved in a different location and keeping it did not effect the fix. 

https://bugsfiles.kde.org/attachment.cgi?id=108162