Hi all.
After 2 hours googling and making a lot of changes in my system path, reinstalling Java SDKs, etc., with no solution, I finally found MY problem on mi Win7 32 bits machine: The last Android SDK tools 23.0.4 have a BUG.
I found the solution here: https://code.google.com/p/android/issues/detail?id=77289
It seems that they packed the 64bit version of find_java.exe in the 32bit package, so is failing and Studio can't detect the right SDK.
In the coment #11 a user provides the right 32bit EXE (you can overwrite the original with that one) for download and after that, Studio begins to work, detecting the SDK.
So, for this time, it's not a fault from our guys, but from Google guys