My car wont start...

I put the key in and turn to start, the electronics turn on, the head lights dim (so i know its not my ignition switch) but the car doesnt start.

When I put a screwdriver across the the terminals on the starter solenoid and have someone turn the key to start...the car starts.

I also switched the ingition relay with the starter motor relay...im not sure why...but i did it and still the only way i can start the car is with a screwdriver.