I had some Android SDK problems today in 2 different computers (where I've updated from 3.1.3 to 3.2.1) but I found the right solution to solve it, confirmed with the second computer after do the same things that on first.
The problem: Studio cannot find Android SDK but the path is right and your API levels are there, on the disk.
The solution: Just go to "SDK Manager" on your Android SDK folder and update the "Android Support Library". I've updated also all the components suggested, but I think it's only that.
Just after the update of the SDK Manager, magically, Studio detected all my old AVD Machines.
But this got me stuck for 3 hours, looking in forums. I hope this can help others to don't waste their time.
