Inside Documents/Witcher 2/gamesaves/ :
Drop your resolution to 1080p or lower (e.g., 1600x1200) to pass the glitch. the witcher 2 black screen after chapter 1
You’ve just made it through the grueling siege of La Valette Castle. You survived the Kayran, navigated the political swamp of Flotsam, and made the pivotal choice between Roche and Iorveth. The loading screen for Chapter 2 appears... and then it hits you: navigated the political swamp of Flotsam