I don't record (or have anything to do with) games, but I've had a look on Debut's Tech Questions and I wonder if this might be of help, even though it refers to "black video" rather than desktop.
"Black" video**
On some machines, Debut can't get access to the displayed picture, which results in the inability to record a game. If you see that the produced video contains audio only, while video is completely black, try switching the game to a windowed mode. It may allow Debut to access the game's screen surface.
I probably can't help with the sound either, but I have ticked "Loudness equalisation" in Playback devices/speaker properties/Enhancements. It may only make the sound you hear louder, not the recorded sound, but it's worth a try.