What can Microsoft do to regain it's crown?

In the 90's to early 2000's Microsoft was the king of the hill. Since then, Microsoft has seen a steady decline in market dominance and relevance. Yes I am aware that Windows still represents over 90% of all desktops. But you and I both know that the big MS has failed horribly in its attempt to penetrate the mobile market and regardless of how you may like or dislike Windows 8, it is not nearly the monster that Windows 7 was. My question to all of you is this:

If you were the CEO of MS, what would you do to "fix" their problems, and how would you put MS on top again?

Examples: Rebrand Bing, Open Source Windows, Buy Facebook and integrate Windows with Facebook on a fundamental level, etc...