I have a 6 month old samsung laptop, at the moments the personalisation themes is unable to select any 'aero' themes (they are greyed out), it is stuck in classic windows look. It was working fine yesterday. It has done it before and mysteriously fixed itself, but I don't understand why. I didn't install or change anything before it happened either time.
I have tried restarting the computer and restarting windows desktop manager and making sure the performance options is set to 'for best appearance'. Using these instructions: https://www.howtogeek.com/howto/windows-vista/my-vista-aero-glass-turned-itself-off-how-do-i-enable-it-again/