I have recently upgraded to ver. 2.0.5, but after first loading Audacity 1.2.6 the output from my Acer Laptop headphone jack, which was perfect, was corrupted to low volume with distortion when playing audio from other sources like a browser. When playing a file in Audacity the quality of the audio through my headphones returns to normal. Along with the program update, I’ve tried re-installing the Realtek audio driver with no change in performance. I have not tried uninstalling the Audacity program.
What version of Windows?
Do you have separate speakers and headphones devices and the default Windows playback device is set to speakers? That could be an explanation.
Is the plug of your headphones clean? Is the headphones port clean? Dirt can prevent proper contact.
Reinstalling Audacity won’t make any difference if Audacity playback is not the problem - Audacity does not modify the sound devices. However you should uninstall 1.2.6 if it is still there as a separate installation from 2.0.5.
Are you sure it’s not just the quality of what you are listening to? Usually sounds streamed over the internet are more compressed (lower quality) than music downloaded from iTunes or Amazon.
And usually, any sounds that come digitally from “inside the computer” have the same “path” and are all controlled by the “WAVE” slider in the Windows playback mixer. So streamed sounds, or sounds through Audacity or Windows Midia player, etc., should all have the same “processing” at playback time, if any.