virtualbox.org

If Aero is not directly enabled, then change the theme to an Aero one. It's usually the first thing that solves it. Most of the time, Windows will stick to it's basic theme after Aero becomes available unless the driver specifically enables it. E.g. when you install the Intel video drivers on such hardware, you'll be asked to enable WDDM or something, which will trigger a change to the Aero theme. If Aero is available, Windows doesn't always switch to it.

yes, done that

aero switches on

and then the problems mentioned above start to happen