I, Aleonymous (I'm not with Stoic or VersusEvil), have compiled the following trouble-shooting guide to help you find solutions, all in one place. The steps are in approximate order.

DISCLAIMER: Most of these "solutions" are harmless and/or reversible. Try any of them freely, but remember that you're doing everything at your own risk!

• Try restarting game > Steam-client > computer
  
• Verify Integrity of Game Cache [Ref]
  
• Linux (only) -- Try linuxfix beta branch [Ref] and, if that doesn't work, try also this extra action
  
• Low-end computers -- Try freeing up as much RAM as possible, by closing unwanted background applications
  
• Ensure your video/audio drivers are fully updated
  
• Windows 8.X and 10 -- Running the game .exe in comptatibility mode with Windows 7 might solve some problems (e.g. crashes)
  
• Partial Black Screen During Travel -- Use the following launch option: "--landscape_buffer false" (without the quotes)
  
• Mac OSX 10.6.8 -- Crashes and no-sound might be fixed by deleting (or moving to a different location) the system folder "/Library/Frameworks/Adobe AIR.framework" (without the quotes)
  
• Taskbar not disappearing issue: Disable "display scaling on high DPI settings" for the game executable (right click on: C:\...\Steam\steamapps\common\tbs\win32\banner saga.exe>compatibility tab).
  
• Try forcing windowed-mode [Set Launch Options][docs.google.com]
  
• Gamepad issues -- Try disabling gamepad detection (gp=false in [Set Launch Options])
  
• Try using the "old" renderer (starling=false in [Set Launch Options])
  
• Replace Adobe AIR runtime that came bundled with the game. Details can be found in [Ref] and [Ref (detailed)]. Attention: Updating Abode AIR itself (a different procedure than the one described) will not help.
  
• Check that Hardware Acceleration is enabled [Known Windows Issues][stoicstudio.com]
  
• Uninstall/re-install game. After you uninstall, make a check that the game directory folder has been wiped, else manually delete it (i.e. delete the folder to the path ...programfiles\steam\steamapps\commom\tbs)

If all else fails, try contacting support@stoicstudio.com. Make sure you include log-files and/or save-games [Ref][stoicstudio.com].

Needless to say that (1) some problems can't be solved and (2) sometimes a seemingly unrelated change might help solve an issue!

Always backup.

Good luck ;)