Sorry..but the ONLY thing you can try before visiting Nokia Care is remove the battery for a couple of minutes, insert it and see if you get thru ' ...
You can also try the three-finger reset :
1) Switch off the phone
2) Press and hold the GREEN button (call button) + RED button (reject button) + camera button at the same time
3) while you're holding these three buttons, switch on the phone
4) phone will restart, hold the buttons untill you see the shake hands image on the display
PS : this also clears all data from your phone, so I hope you backed it up.