no internet after random period

I've read about this problem around these forums but mine is a bit different. I have Windows XP Pro SP3. After a random period of maybe 30 mins to a few hours, my internet connection seems inexistant. PC reacts like there is no internet cable plugged in. I've checked the ipconfig command in command prompt before my internet shuts down and after and there was a change. A few lines(IPs) were missing after my internet fell.

Does anyone know that my problem is about and how can I solve it??