I actually encounter the same problem as you.
on Windows 7 Pro
Motherboard Intel i5-2500K CPU @ 3.30 GHz
Realtek High Definition Audio
Nvidia GeForce660 GTX
Everyt material of my comp are from Gigabyte
here a screen of my Graphics setting in GW2
http://image.noelshack.com/fichiers/2015/07/1423663657-gw001.jpg
