I've had this game for a week and it was running smoothly in 1920x1080. I played earlier this morning and it was running fine. A few hours ago the game refused to launch and whenever I start the game the screen would flash white but the game would not launch. I restarted my computer and since I've done that the game has been running very slowly on the 1920x1080 resolution.

I tried different resolutions and the game worked fine but on the native resolution the game is running slowly even though I didn't have any issues with the 1920x1080 with the game before today.

(Re-)installing the Microsoft Visual C++ 2010 Redistributable Package (x86) might help, see here:
http://www.gog.com/forum/hotline_miami/hotline_miami_massive_slowdowns_slowmo_mode_help_appreciated/post2