The “Cannot set display mode” error is a rite of passage for Serious Sam veterans. It looks intimidating, but it’s almost always a fixable configuration issue. In 90% of cases, using the +fullscreen 0 launch option in Steam will get you back to gibbing Werebulls within 60 seconds.
: Run the DirectX End-User Runtime Web Installer or find DXSETUP.exe in the game's installation folder and run it as an administrator. serious sam 3 cannot set display mode top