i can go online on firefox, but not safari

i posted this from firefox and the net works fine on this browser, but when i open safari it tells me it cant connect to the server of any website and ive tried this for multiple websites. also any online based apple apple services dont work and cant connect (eg, iTunes store, software update.) i have the internet connection so why wont safari connect. i'd really like to sort this out because safari is my browser of choice

and i have another problem. msn messenger always tells me i have a wrong sign in address or password. when signing into live mail the sign in works fine so why is messenger rejecting it?

Is the Mac getting an IP address that is right for your network? All this broken stuff is a sign of some major misconfiguration or broken software component.

It might be down to 'proxy' settings. I think Safari uses the proxy settings it finds in your (system) network settings, while Firefox has the ability to use its own separately configured proxy settings.

Go to System Preferences -> Network -> Advanced -> Proxies and check the settings for Web Proxy (HTTP). Then compare this to the settings in Firefox by going to Firefox Preferences -> Advanced -> Network -> then click on the settings button in the Connection section.

If the two sets of settings are different, then change the system network settings to match what's in Firefox.