Lumia 620 Error: Unable to find a boot option

hi anybody anyone who hopefully can guide me with his/her great skill, actually im facing an error on lumia 620 which i used very careffully even i dont put a memory card in it.Nor i ever place my mobile with a mobile repairer but one day i just saw a status of my friend on whhatsap after that my mobile hang up and shut down automatically and after that it just show that error after Nokia logo. ERROR: unable to find a bootable option.Press any key to shut down i search microsoft forum no luck i try recovery tool no luck and at last i contacted microsoft personal he suggest about Nokia franchise shop.But i guess they will suggest me about 200 or 300 $ for its repairing.On which a new mobile can be bought.So anyone out there could give me a better solution as i already lost my course studies in adobe reader and some of important books.
Please if any one know the hints.
thanks