What version of Sound Forge 15 (Pro or Audio Studio) ? Is the latest build installed? Does this happen with PCM <.wav> and other file types (or just MP3 files for instance) ? Is there a plug-in chain applied to the timeline.
Peruse **IMPORTANT!** - INFORMATION REQUIRED TO HELP YOU from the Vegas forum, a lot of the basic info is universal to Sound Forge. Automotive analogy: If you call a garage about your car, it is not enough to say: "My car has stopped working".
With the limited information, I can only recommend resetting Sound Forge @samuel-mattos . In the 'File' menu. select "Reset and clear cached data". Close and restart Sound Forge.