After managing to get into a single player game, the game is extremely laggy and almost impossible to play. Using the mouse while playing works, but after trying to exit from the game via the menu, clicking on the "suspend" button made the game to crash. Remember I was running this game perfectly fine yesterday with no lag at all.

EDIT: I also reinstalled the game, mouse bug and lag still occurs.

Please provide dxdiag.txt . Is this happening in any other game?

Make sure you have latest sound and gpu drivers installed.
Also have you installed any new software since you played Arma III without issues?

Other games work fine, no software changes.

From the Dxdiag file i can see that you dont have the latest nvidia drivers for your GPU, Please update to the latest drivers ( with clean install) please.

Drivers updated, mouse issue still occurs.

Are you running development build of Arma 3 on Steam? Have you connected any new piece of hardware?

Try deleting Arma 3 Alpha folder in Documents and try again.

Deleting the folder in Documents worked, thanks!

Closing