Can a Mac computer with only has Windows installed be encrypted with Symantec Drive Encryption?
During the installation of the Windows operating system on Mac hardware, the Windows installation disk is used to remove all partitions and then creates a new partition for Windows to be installed on. If the disk is then encrypted with Symantec Drive Encryption on the Windows partition, the operating system fails to load after entering your passphrase at the Encryption BootGuard (pre-boot authentication) screen.
“missing operating system”
This is not a supported configuration on Mac computers with Symantec Drive Encryption.
Even when removing all partitions and then creating a new partition during the installation of Windows, the Mac OS X system protects certain elements such as the EFI partition. Therefore, simply installing the Windows operating on Mac hardware and then attempting to encrypt the drive will fail. The only supported method encrypt Windows on Mac hardware is to use the Apple Boot Camp Utility and then perform Symantec Drive Encryption from the Mac OS X partition.
See the following article for using Boot Camp with Symantec Drive Encryption:
Note: If Windows will be the only operating system that is desired on the Mac hardware, it is necessary to install Mac OS X, even as long as there is a minimal amount of hard drive space and then use the rest for the Windows operating system partition.
Once the Mac partition and Windows partition are created, you can configure the system to always boot to Windows when you turn the machine on. This should be done with the Boot Camp utilities.