I know you cpu supports VT-x. I think it your mobo bios which is old. I think bios update will solve the problem.
F5 bios has new cpu microcode for Wolfdale, which is yours. Updating F5/F6 bios will solve that problem i hope.
But why you need VT-x enable? For multiple OS?
Thanks Mubin. I´m going to update F6 this afternoon and I will tell you the result
I need VT-x for virtualizing 64 bits machines.