Everytime Dayz crashes (which is everytime I open it, btw), the game will refuse to launch again as steam states that dayz is already running. It also shows all my friends that I am playing DayZ, WHILE I'm clearly playing with them on a different game.
The only solution I have found is to kill the steam PROCESS (not the application, the process/.exe), using task manager.
I can then proceed to launch Dayz again, have it crash in the server select screen, rinse and repeat.
EDIT: forgot to add, the only process related to DayZ in both the processes and applications tabs of the task manager is Steam. There is no Dayz application running at all. this is the only game that I experience this with.