do you guys know where the previous flight is stored ? maybe if I delete it I can fix this problem

did that - the fuel is back to normal, the flight started with the engines dead and a click click noise when I tried to restart the engines

It is not the default flight, something happens when an aircraft crashes that when FSX restarts I find myself with a dead aircraft on the tarmac.

I am thinking maybe FSX saves the last state to some file that I could delete to restore it to zero condition

Are you running FSX with FSUIPC. FSUIPC is what creates the previous flight save. You can safely delete it  when you got the sim running, as Boikat said: all you have to do is open the "Load" find the saved flight and delete it. Or you can delete it from your: My Documents/Flight simulator X Files, just remove all three files that say previous flight.

What I belive most everyone does here is make ther own default flight, so you start with a cold/dark aircraft everytime....just creat a flight shut everything down  and name it something to your liking, click the save as default and your good to go. BUT, all good pilots always check for fuel before start-up