have a 3gs 8g running off ios4.3..... jailbroken win jailbreakme. got home tuesday evening and screen went grey/black as i removed from car charger when i checked a few minutes later was dead. tried putting into recovery and dfu several times and phone was not recognised by itunes but laptop did recognise usb connection at first but not now. back of phone get warm when on charge but no other sign of life.
anyone got any opinions.

Similar things happen to my phone. I guess as long as the battery is getting warmer it's safe to say that the charging portion of the device is working. I think I have a dead logic? board.

Most likely a dead logic board, and if the phone is relatively new, it would be covered under warranty. Take it to an Apple genius bar and they should repair or replace for you.