After I rebooted the vm, changed some settings (attached a dvd drive), it would boot up again. I have had the same happen in a strange instance from removing an ISO from the dvd drive while the VM was on, then rebooting it.
If you receive this error notice:
Failed - The attempted operation cannot be performed in the current state (Powered off).
Then do the following:
Right click the effected virtual machine, select unregister, then confirm by clicking ‘Yes’.
To re-register it:
Click ‘Create / Register VM’
Select ‘Select one or more virtual machines, a datastore or a directory’
Navigate to where the .vmx for the VM in question is, select it, then click ‘Next’ and and then ‘Finish’.
The VM should now boot normally again.