What do you do on Plants vs Zombies when it wont work anymore and just says failed to open file do i have to delete it all?

If Plants vs. Zombies is showing a "failed to open file" error, try restarting your device first. If that doesn't work, check for any available updates for the game or your device's operating system. You can also try reinstalling the game, but make sure to back up your progress if possible. Deleting it entirely should be a last resort if other troubleshooting steps fail.