Guild Wars 2

I meet all the requirements with my pc for the 64bit version and then some, but the game wont start at all. After i log in and click play it just stays at a black screen and i can only get out if i go to the task manager and end the process of gw2-64.exe. What could be causing this?

can someone please clarify to me how to switch back to the 32bit version on command line promt, if possible.