Do not modify your DNS settings within the Plesk panel unless you need to do so for a specific purpose and you know how to modify these settings.
For example, do not click the button that says "Switch", as this will switch your zone from Master to Slave. It will not allow you to change the nameservers for your domain. You must change your domain's nameservers via your registrar. If you click this option and your domain is pointed to our nameservers, it will stop resolving. If this occurs, you will need to click the option again.
If you need to disable your zone file (ONLY because you are pointing to our IP using DNS records), you can click the on/off button.