Enable hidden hardware virtualization settings
Although many sources claim that virtualization works on your model, it's not an absolute certainity.
According to wikipedia, the Athlon 64 X2 4200+ has two models with part numbers ADA4200DAA5BV or ADA4200BVBOX. This seems to be a confusion - there seems to be only a single model.
The site products.amd.com elaborates some more, detailing both the above numbers, but calling them rather OPN Tray ADA4200DAA5BV
and OPN PIB ADA4200BVBOX
. It also says
"Virtualization : No".
To further verify the issue, you may use either SecurAble or Microsoft's Hardware-Assisted Virtualization Detection Tool (made available by mydigitallife).