Err... if you don't even know what's missing, it can't be something you were using? Unless you accidentally uninstalled the entire application it should still be in your Start menu somewhere.
As far as how it happened... you probably unpinned it accidentally. If you right-click an icon, the "unpin" action is the one at the bottom of the menu, closest to the mouse pointer. Not hard to hit that by accident, and it doesn't ask you to confirm the removal. (I'm assuming Windows 7 here.)
just had a look through the start menu, and it was the windows media player icon, recognized the icon cause it was beside my vlc icon, and my family too dumb to know that.. sry to say
so now it's all good
Win 10 InWin 303 Asus z170a i7-6700k - H60 G.Skill 2x16GB 2400 M.2 950 Pro 256GB EVGA GTX 1070 FTW EVGA Supernova G2 750w Acer XG270HU HD 280pro