Do PCM <.wav> and other audio file types playback normally? .. Do the files playback in other applications and players.. you could try resetting SF to the default settings which also clears the cache. or reinstall. I would first reinstall the AAC codec (Quicktime).
btw, welcome to the Magix Sound Forge user community.
I figured out the issue. I had a Windows Update before the problem started. Apparently either it or the SF reinstall switched the speakers I was using from my speaker/mic combo to the original default (which I'd deactivated). Things seem to be working fine now.