I've noticed this problem has occurred quite a bit, as it happened to mine as well. However i just fixed it and if anyone has got this problem please try this as it solved my problem.

-Turn your phone on until the message comes up.

-Tap the screen until it goes away and then set it to offline mode. (Tap the notification area/system tray next to the clock and it should be on the right)

-Plug your USB charger (USB end) into a USB that is on, like a pc usb or game console usb.

-Then plug the charger into your phone.

-When the mass storage and pc suite selection screen comes up, don't click either and turn off the phone.

-Once turned off, make sure it is still charging by checking the orange LED pulsating.

-If it's not then do this all again and make sure it is.

-Now turn the phone on, and exit offline mode when prompted to. If you are not prompted by the time you reach the desktop, turn the phone off and repeat until you are. (after the 3rd attempt try enabling it normally via the notification/system tray)

-If it says you've got a 3G signal then you should be connected to your network. Before doing anything, text message yourself and await the reply, or ring your network to confirm it is working.

i hope this helps.

Tips:

Make sure your phone has the latest update package. You can get this via the nokia software updater on the website. However this doesn't always work. If not then connect to wi-fi on your phone and go to the app manager. Make sure the extras and other extra repository things in the application catalogs are deleted or disabled if you have added any. Then update by selecting update all rather than the manual selecting the update or you will be greeted by a "OTA update is unavailable" or something similar.

Also, call up your contract supplier and get a refund for the months you haven't been able to use your phone. So for me that will be 5 months of £40 payments. I was also offered a free extension of 5 months to cover this.