Anything anyone creates is by default copyright; a company hiring to have art made typically buys all rights to the work (Microsoft certainly would).
So, only they can give permission to use, and you can't legally use it unless you have that permission from them. If they have given open permission to use their icons, that'll be posted somewhere official, though I have no clue where they'd do that.
Two cases where that's not true in the US, and you can go ahead anyway:
1. If your game is specifically a parody of Microsoft, or a parody of something broader that includes them (like the computer industry).
2. if nobody makes any money and Microsoft loses nothing. Which is tricky; if they can claim your use might even potentially be part of making their icon set "generic" instead of "their product identity", they can say they're losing something.
Ultimately, though, if they notice the use in an official way (as in, see it and think it's worth bothering over), you'll likely get a Cease & Desist order. This is unlikely, but you Do Not Want to play lawyer games with a company like that, so prolly not worth the risk.