Hi,
Do both sound sources, the microphone and desktop, sound good separately?
Are you singing on the mic, along with music that is playing on the desktop
OR
Are you talking on the mic, while a soundtrack plays in the background?
If singing to music, a first guess is that the mic and desktop sound are not in sync.
Go to Edit, Advanced Audio Properties, and try delaying the mic or desktop sound to get them in sync.
Start with 20 millisecond increments to rough in the delay and see what sounds better, then
smaller increments to get it as good as possible.
This is also where you can delay audio(or occasionally video) to get image/sound sync.
Or you may have some completely different issue...
Thanks and good health, Weogo