How to fix engine electrical problem: I believe there is a short, drained a new battery, and doesn't start the engine. The alternator and the starter has been replaced recently. I would like to know if the starter relay may cause this problem. Many thanks for your help.

Do you have any aftermarket electronics installed on the car? Are you certain there are no lights being left on after the car is shut off? I know this is an elementary question but I always ask. You'd be suprised the things you can forget to turn off, especially on older vehicles that don't have the automatic functions to turn off electronics like newer vehicles do.