I have just got an iMac 21" and it continuously freezes when it goes to sleep and also when the internet is trying to load, i have tried three different browsers but it still does it (safari, google chrome and firefox), does anyone know what is wrong?

To fix the freezing when sleeping problem go to System Preferences>Energy Saver and set 'Computer Sleep' to 'Never'. It seems there is a problem for some with Bluetooth failing to wake after sleep. This fixes it 100% for me and many others on here, until Apple issue a software update to address it.

Not sure what to suggest on the internet problem. I assume you are connected and receive and send emails OK.

Edit: To try to troubleshoot the internet issue maybe try turning the Firewall off: System Preferences>Security & Privacy>Firewall tab.