Thanks for your help Gavin!
Well, I tried the "Diagnose" several times already, but this didn´t help.
I don´t understand what you mean by manually putting in the ISP´s? DNS? What is that?
I tried typing in the commands flushdns and registerdns, but the problem stayed the same. The ipconfig/renew is not accepted. It sais then, that it can not change anything on a Wireless Network when this network is not connected..... I do not understand this, as I am not trying to connect any wireless connection. After 2 minutes, the message appears saying: A problem occured while renewing this interface: LAN-connection, cannot contact the DHCP-server. Request has expired.
I tried connecting directly to my modem and by using my router, however, the problems remains the same....still no internet for me....