dell studio 1735 hdd cable issue

Hi new to this after some help please cause it driving me mad lol...

Dell studio 1735 - very nice laptop works fine apart from the following issue..  it will not switch on lol..  screen flickers and flashes then nothing..  However if i remove the sata hdd cable from the motherboard it boots fine .. but obviously stops on error no hdd found..  i have replaced the hdd AND the sata cable (( the small cable that gowes on the hdd then to the motherboard.  ))  replacing both these does not help.. still has same issue..   please help urgently!  as have lots n lots of work and accounts etc on this laptop...many thanks in advance ...