mobile

I noticed that network coverage lost, service disabled was displayed. I put in different SIM card - no success. Checked IMEI - unkonown. Can't enter mobile network preferences(grayed out). Tried to reset through software, nothing happens. Then tried to reset by holding power+down key and after logo flash release power and press again power does'n work. I tried different combination, nothing happens. Then I entered 3845#*802# and when trying to to reset from there - again nothing happens. Tried to select network type in *#*#*#4636#*#*#* and it is changing back to unknown. Phone seems to be very slow and 4636 code needs some 5 minutes to start working.

What could be wrong? I'm out of warranty and have phone only 6 months. I haven't been messing with roms or rooting.
Model:LG-D802
Software 4.4.2
Kernel: 3.4.0
Build number KOT491.D80220f