Internet not working

I have a Dell optiplex PC Os windows 7 professional . Suddenly it cannot connect to the Internet. I have tried Firefox ( my dedault browser) and chrome. My router shows that broadband is connected and my IPad also connects so it would appear to me that something is wrong with my PC. I have removed and reconnected the plugs and also rebooted but all to no avail. Can someone please help me.
Thanks
Nita