this happened to me twice,it turned out there was a smudge on the dvd installation disc did i say dvd and disc?
maybe remove the HDD completely and put it back in. Check if there is a "master / slave" jumper or auto that might be off the drive. Kick your brother in the (UNPLUG FIRST! the pc not your brother! lol)
thanks all for answers, the cables are ok, when the pc turns on and the cd starts to work for format the hdd makes some noise every second like trrak trrak .. trrak trrak .. trrak trrak ect. i think the hdd is down..