Voice comes on but nothing on screen
Duolingo works fine on my laptop but not on my desktop.
What do you mean "nothing on screen"? I assume you're NOT talking about the "type what you hear" questions?
Does it happen with every question? What if you turn off the "speaker" setting? Do you stop getting the kinds of questions where this happens? What happens if you restart your browser?
And finally, what is different between the laptop and the desktop? Are you using different browsers? Operating systems? Versions of browsers or operating systems? Do you have certain extensions installed on one but not the other? Does one use wifi and the other use an ethernet cable, or do you maybe use one in a completely different area of the house? You get the picture--if it's working on your laptop and not your desktop, then explore that difference; you'll probably find the solution or at least a fix.