cant access internet from LAN

Hi all,
I am having intermittent trouble with internet connection in my LAN. The PCs connect via a web server, and frequently the internet connection seems to drop for about 10 mins. But when I connect via a remote desktop to the server… the servers internet connection is fine! Ive changed firewall settings on machines, changed the patch leads to the server, switch and router and reset the router on numourus occasions…. any ideas?