A method and system to switch between a Service virtual machine (VM) and a Guest VM in a virtual machine monitor (VMM) of a computer system. The VMM is loaded on the computer system to support a Service VM and a Guest VM. The Service OS is booted in the Service VM during the pre-boot phase. The Guest OS is booted in the Guest VM of the computer system. During OS runtime of the Guest OS, a VM switch is performed from the Guest VM to the Service VM without rebooting the computer system. The Service OS includes diagnostic tools to analyze the Guest OS. In one embodiment, the VM switch is performed by firmware of the computer system. In another embodiment, the VMM operates in accordance with an Extensible Firmware Interface (EFI) framework standard.