The problem is DR isn't very user friendly at the moment I guess.
It's installed (most likely) but it creates no shortcuts. You'll have to go exploring through your computer to find it. Go to "My Computer". Assuming you didn't change the install directory, it is installed to the place wherever you downloaded it to.
Run a search of your computer for "DragonRaja.exe". Or you can go through the folders in your computer and look around for it.