First verify the SIM is properly seated, try using another SIM to verify.
Try a reset (search the forum for precautions) using Settings>about>reset my phone
If all else fails go to a Nokia Care point
Click on the blue Star Icon below if my advice has helped you or press the 'Accept As Solution' link if I solved your problem..
20-01-2013 14:20 - edited 20-01-2013 14:47
You can also take the phone back to the shop which sold it to you , or a branch of your network supplier if you're on a contract; both of which are supposed to have provided a phone that works.Nokia Care is an additional support, it doesn't supersede your statutory consumer rights and there may well be no Nokia Care centre anywhere near you.