Whats wrong with my acer laptop?

i was gonna watch a movie online but i accidently downloaded something. now my laptop is really slow, the mouse lags, most pages dont finish loading so they crash, and internet explorer windows randomly open up with different ads. once in a while it goes back to normal but only stays for like 10 minutes. it the same whether on balanced mode or high performance. ive already updated and it didnt make a difference.