Cisco 851W Router keeps losing Internet Connectivity

I have a Cisco 851W Wireless router which i configured using one of the templates on this site. It works fine for about 2 hours then loses it s connectivity. I can’t connect to the Fast Ethernet port from either a wireless get it started again is to power down the router.

I’ve noticed that when this happens if i plug the PC directly into the cable modem all is fine and i can get an ip address and connect to the internet. It appears the FastEthernet port is losing it’s connection for some reason.

There is a similar problem recorded on this site however a power down does not resolve the problem. Has anyone come across this and is there a resolution. The router itself is only a month old.