GAME FREEZING WHEN I WIN/LOOSE A GAME

Hey guys, i got a problem, whenever i win or loose a game i should see the nexus exploding, but i dont, the game just freezes right before i should see the victory/defeat sign...then if i want to change to some other thing with alt+tab or if i want to close it with alt+f4 or ctrl+alt+def i cant open any of these and they dont work... only alt+f4 shows me what im about to see but when i release it it doesnt show anything... just screen turns black... when i ctrl+alt+del, it shows me the thing where i select program maneger and it doesnt open it(i mean it does open) but i cant see it....soooo does any1 of u know how to help me? i would really appreciate any help, couse i dont really wanna turn off and on my computer every single time after the game finishes.... the backup plan could be just to turn off league but i dont have any idea how to do it( i only know the 3 ways listed on top)...oh and it started happening with the previous update(today)... if any1 can help me i would really apprechiate it.. thank you!!