In terms of being a successful and profitable business, Microsoft is the pinnacle of achievement for any entrepreneur to achieve. Not only is it one of the worlds largest companies and the leader in its field, but it has made its owner Bill Gates, the richest man in the world today. So wanting to take over Microsoft is no easy task to achieve certainly, and you would have to have billions of dollars before you think about even coming close to being a major shareholder. As the old saying goes, you cant buy something that isn’t for sale, and Microsoft certainly isn’t looking for new people to run or own it.
As with most large companies today Microsoft is floated on the stock exchange. This in theory means that if you had enough money you could potentially over time buy enough of the shares to make yourself the majority shareholder (51% or more). This would mean that you were the effective owner, and from being the majority share holder you could then force out the other major shareholders and eventually own all of the company by yourself in effect.
You would also have to have a lot of political power and influence to make all the other shareholders sell or trade their shares with you. Which again is something that takes a lifetime of being a successful businessman as well as shady dealings with authority figures to achieve.
The reality though is somewhat different from all that. Not only does Microsoft already have several major shareholders that each own significant portions of the company, but it has the richest man in the world as the owner already. In which case, why would he want to sell his won company that he has nurtured for years to you. Who likely knows nothing about running a massive multi-national company, or about software development. He wouldn’t of course, which is why it would be very difficult to ever buy Microsoft, even supposing you had the financial recourses to do so.
The problem of what you would do when you did own Microsoft would come next. Unless you are of a similar mindset and knowledge level about computers that Bill Gates is, then you wold likely see the company that you had just bought slowly fail. A lot of what Microsoft has achieved has been down to Bill Gates himself, his vision, and his ideas. Unless you could match those then the business would son be worthless anyway.
The only rational way that someone else will ever buy Microsoft is that a few years down the line, Microsoft many not be the leading software company in the world. This wold mean that the owner of a larger company might have enough power and wealth to buy Microsoft and make it a part of his own holdings. For example if Apple becomes a much bigger company than Microsoft in a few years time, then conceivably the owner of Apple could buy Microsoft.
A better idea that trying to buy Microsoft would be to start your own company in a similar vein. If it was successful you could become larger than Microsoft and buy it out. If Microsoft saw you as a threat then it might buy your company, in which case you could climb the ladder of power from within to owning Microsoft.