Jarow? Versuch mal folgendes (aus dem EN Forum, hat mir geholfen).
This is most commonly caused by the patch server hosting corrupted files, causing GW2 to infinitely download them as it never gets what it expects. To fix this, you have to edit the hosts file to manually select a patch server:
Press WindowsKey+R, paste the following, then press CTRL+SHIFT+Enter to run it as an admin:
notepad %windir%\system32\drivers\etc\hosts
Add the following line, then save and launch GW2:
3.92.131.16 assetcdn.101.arenanetworks.com
Remove it when you're done. Ideally, you only want to use this while you're stuck, as it will likely be slower depending on your location (this is the primary US patch server).
For future reference, the IP changes roughly every patch; to find the current one, open cmd.exe and enter:
nslookup origincdn.101.arenanetworks.com 8.8.8.8