Why do I keep losing internet connection?

I have wireless internet, I am using a Cisco router. Every once and a while I will just loose internet connection. It says I'm still connected to the router but that I do not have internet access. I then go and unplug the power and Ethernet cable from the router and then plug them back in and it usually comes back on. Sometimes I have to do it a few times before it works again. So, why is it that this happens and is there anything I can do to fix it?