Keyboard mouse input lag

What's causing this problem, every game there's always that 2 min problem of this lag where my abilities no longer respond to my keys, for example I press F to flash it takes my champion about 15 seconds to do that and than he follow it with the random abilities that I wanted to use back when I was in fight my team looking at me throwing skill shot everywhere and flashing for no reason makes me look like troll. What is happening to my game the champions tab even got stuck on my screen so I had to fight for around 20 seconds with that tab opened on my screen I couldn't see anything did I also mention that the summoner's rift music and announcer voice also cuts it's like lagging