My 2001 Land Rover Discovery isn't unlocking and the engine won't start.?

I'm looking for any advice all of you experts can give... thank you very much! I need some help with my Land Rover Discovery series II 2001, the car is run fine, but one day, I stop on a red light and the engine turn off, I was able to start the engine back on, but later the same day I had the same problem. And the next day the car won't start any more we are looking for some technical expertise as to thoughts why my 2001 discovery II is not starting any more. If it is a Fuel Filter - where is the part located in the vehicle? I think it might be the fuel pump, but I don't know where is located. Could it be an oxygen sensor? Thank you in advance for all your support that I can get.