[CLIENT] Client and whole PC freeze the first ~30 seconds after logging on

I think it started back in patch 5.5. After I login my whole PC freezes for ca. 30 seconds. I saw it happen on another PC too, that had a whole different hardware configuration, so I think that it's not hardware related. And also after the freeze, any news link/shop item inside the client misses the thumbnail. My PC isn't that fast, but before the latest patches that didn't occur once, it started recently.

Configuration, if needed: Intel C2D E7500 3GHz 2GB RAM ATI HD5450 512MB Graphics card Mobo is ASUS P5GC-MX/1333

P.S.: This ONLY happens after the login, anything else I do on the computer doesn't freeze the whole system.