've unpluged the switch and plug ethernet shield directly to the computer and nothing happens.
If you connect the ethernet shield directly with the pc then you need to use a cross over cable.
I suggest to use an ethernet switch or ethernet hub.
It looks like you have a networking problem and not an arduino problem. >
Please try to connect a second computer to your network and then ping this computer. If it doesn't work you have to solve this networking problem first.
Generally it is pretty easy to run the ethernet shield on a working network. For the first test you should always use the sample sketches from the arduino website.