Ethernet shield seem to reset itself

I just bought the Ethernet Shield KA04 kit and after some assembly and soldering and after installing the libraries and run the KA04_sample_code it runs fine a few seconds, displays the available IP gateway and router for a few seconds then seems to reset itself and start again after 15 or 20 seconds, or the webclient turns to loose information and show page not found… what can be happening??? seems kind a unstable and weird behaviour … can you help?

Thanks in advance