No Service. Help!

[minisean]

Hi, The phone icon at the top (next to speaker, battery, etc. icons) displays an exclamation mark (!), and when I tap it, it says 'No Service'. I clicked on Settings and went to the Network tab then clicked Find Network, but it still doesn't connect to any network. However, it still shows 3 or 4 signal bars when I tap it for the first time and then it brings up the larger icons, but it doesn't connect to the network.

I am on Orange UK, and the phone can connect to GPRS / 3G, but not to the actual network.

Sorry if anything is unclear btw

Thanks in advance :)

EDIT: Sorry, just realised I posted this in the wrong forum.