Windows freez while connected via ethernet cable to router

Hello, I have an annoying problem with my pc running Windows 7 Ultimate. Till I connected my pc(which is a desktop *without* wi fi adapter) to internet using a* ethernet cable* and a* wi fi router* I had no problems. After that, randomly, but especially when browsing the internet, the computer freezes and I must restart it. I have to mention the fact that if I connect my pc to internet...