BMW 330d Fault?

Hi there could you please help me
I have a BMW 330D 53 model, went out to the car this morning and the dde light and others were flashing continuously, car wouldnt turn over.
My thoughts were that it could either be the battery or the fact i only had 20 miles left on the clock and due to being -7C the remaining deisel may have frozen.
so i put 5 litres in from the garage, still didnt work.
tried jumping from a mates car, didnt work.
disconnected the battery to try reset the computer and since then nothing works on the car except the airbag light and also the keys do not now work either. any ideas pretty please.