You cannot start virtual machines on a computer that is running Windows Server 2008 R2 and on which a CPU is installed that supports the AVX feature

Si estas en HyperV y al iniciar tu VM te sale el error:

You cannot start virtual machines on a computer that

is running Windows Server 2008 R2 and on which a CPU 

is installed that supports the AVX feature

Debes de estar en WINDOWS 2008 R2 y debes instalar el SP1.

Solucion: Instalar el SP1 de windows 2008 r2, mas detalle en:

http://support.microsoft.com/kb/2517374

You cannot start virtual machines on a computer that is running Windows Server 2008 R2 and on which a CPU is installed that supports the AVX feature