my two VM instances for two web hostings down since last 36 hours

[karuntogaru]

Failed to start wordpress-1-vm: Operation type [start] failed with message "The resource '64647589655-compute@developer.gserviceaccount.com' of type 'serviceAccount' was not found."

[alexmoore]

It seems these two VMs are configured to use the default compute engine service account but that the service account may have been deleted?

You can read more about the default service account here: https://cloud.google.com/compute/docs/access/service-accounts#default_service_account

It may be possible to restore the account by following the instructions here: 

https://cloud.google.com/iam/docs/creating-managing-service-accounts#undeleting_a_service_account

Alternatively you can create a new service account with the required permissions and update the VM configurations to reference the new account, or if your VM does not require a service account, then you can simply set the VMs to have no service account.

Service accounts are used by applications running on VMs to programatically interact with Google Cloud APIs and services, so if that is not something you are doing it may not even be needed.

This is also a great resource to learn more about service accounts: https://cloud.google.com/iam/docs/best-practices-service-accounts