if it's under warranty, dont do any restore or update. try to contact your dealer.
NOTE: This is only for 5800 with V. 20.0.012
1. With your 5800 turned off,
2. Press and hold [Green] + [Red] + [Camera] Keys
3. Turn phone ON, and keep pressing it until you see the Nokia Shaking Hands Logo.
The Default code is still 12345, of course...
Do this if your device is not turning on properly or better yet bring it to your nearest Nokia Care Point.
Warning: This reset code will delete all data from the phones memory.