Whats wrong with my computer?

recently i had a torrent downloading on utorrent and left it on over night, i knew it was safe because my friend told me to download it and since it takes really long, about 1day i should just leave it on over night like he did, so i did and the next morning my screen saver was on and i moved to mouse to turn it off, when i did nothing showed but my background image, no icons no start bar nothing, and no its not where you can make the start bar hide its just all froze up, but whats even weirder is that i can still access all of my programs i just have to use ctr+alt+del, so what do i do to fix this or do i have to re install windows?