1. Delete Addons and Data folder on your computer + verify files with Steam.
2. Delete DayZ folder in My Documents on your computer + verify files with Steam.
If you are unsure how to verify your files with Steam; here are the steps:
1. Launch Steam
2. From the Library section, right-click on the game and select Properties from the menu.
3. Select the Local files tab and click the Verify integrity of game files... button.
4. Steam will verify the game's files - this process may take several minutes.
5. You can monitor the progress in the Steam Downloads section.
