Keep in mind I don't really know what exactly happened, so I just post what I did before it happened.
Crash to desktop:
- Go into the editor.
- Create a mission. I was actually working on a almost complete mission.
- Preview it a few times. The game crashes to desktop with the message "graphic drivers stopped responding and have been restored".
Total lock up of computer:
- Play on a server for some time. I played for about 45 minutes.
- Leave the server and go back to the main menu.
- The main menu and mouse pointer became rather laggy and at a certain point the computer locks up totally - requiring a hard reset.