My 05 chevy cobalt has the code p0171 and now wont start how can i fix it why would it not start all the sudden

Hello, a P0171 indicates a lean code that could be due to lots of air getting into the intake without being desired (vacuum leak, mass air leak), or a wiring or sensor issue with the pre-catalytic converter oxygen sensor. Testing is required to see what is going on; alternative fuel (propane, cleaner) is used to spray around the intake while monitoring engine performance to see if a leak is present. Also, the sensor can be monitored. Your mobile mechanic does not appear to be properly educated or equipped to diagnose or repair this concern, so seek additional professional guidance from a local trained technician with the proper equipment and know how.