WotLK not opening at all

Hey guys!

Im having problem with my client as it is not opening WoW at all. My screen just flickers couple of times, leaves WoW running but not opening it, not even in a window. Is there any way to solve it or what? I freshly downloaded it from here obv. Also, the sound plays normally in the background from the login screen, but I cant access it due to the flicker. After the flicker it just returns to my desktop and nothing happens.

Thank you in advance! :)

Update:

A little clarification, the sound is not running in the background, my mistake. When I briefly click the WoW icon in taskbar, it plays for a few seconds and then closes the window, still leaving WoW running with no visual.