Loading screen freezes

When I try to enter or leave a battleground or an arena, the loading screen freezes and I can't do anything. Then I have to unplug my computer and it is so annoying to do it everytime the screen freezes. Sometimes when I do enter a battleground, something gets wrong with the environment, for example: I enter Twin Peaks and the river is all white with no details or anything, just a white line. When that happens I know that the screen will freeze when I try to leave the same battleground. Sometimes I enter Twin Peaks again and the river is normal, then my screen won't freeze when I leave the battleground. In most cases when I try to enter or leave any battleground or an arena, the screen freezes. Does anyone know what is wrong? Please help me.