imei not reconised on iphone 3gs says connect to itunes

one min my iphone was working fine. dropped it and now won't turn back on.The only way i can is via the mains charger, but then the screen asks me to conneect to itunes and also says my imei and iccid are both unknown. And when i do disconnect it from the mains and then connect it to itunes it turns off straight away and doesn't get picked. Heellllllp please.