Black screen after champion select

i used to have the old client and everything worked just fine, when the new client emerge i upgraded but in the new client te game just didnt work well to many bugs and in-game i always had the black screen, now that the new client is permanernt i cant play, after the champion select everything goes black and i can just see the cursor on screen, i can move my champion but cant see nothing, i know that because my friends says that it move to where i point.

help?????