Is it possible i need a new ethernet cable ?

Is it possible that my extremely slow loading web pages are because I need a new ethernet cable ? I've tried everything I can think of ( system restore to a date everything was running well. Updated anti virus and spyware, etc....) my diagnostics say I'm running at 100mbps, but I can hardly do anything when I try to access many web pages. Is the info maybe not streaming from my modem thru the ethernet cable to my pc ?