The only way I know to turn Aero back on is to run the Aero troubleshooter. There is no Themes list menu as in Vista, XP.
Did you check which Windows Updates were given prior to the problem?
Did you attempt to roll back Display driver
, or reinstall? THere may be several to try in Device Manager>Display Adapter>Update Driver>Browse my computer>Let Me Choose list where they are stored.
As a last resort I would try Capt. Jack's advice to run a Repair Install.
And since you did an inferior in-place Upgrade, which imports Vista corruption, I would consider a formatted clean install from boot in your future.