I feel this, when I was a young lad playing in 2015, I was not tech savvy. I would click on league's shortcut for it only to do n o t h i n g.
Me, not being the computer wiz I am today, decided to re install league every time to fix the problem.
Now... reinstalling league today takes about 20 minutes, and that's manageable. However, back in 2015 if you wanted to reinstall league, you were better off reinstalling before you went to bed so that you wake up with 30 mins remaining to make breakfast.( I was committed) This repeated until my older brother( a much wiser individual) educated my dumbass about Task manager.
I've gotten a new computer since, so I don't run into this problem as often, but I definitely think it is worth looking into.