Need to isolate the cause down to fuel or ignition, are the injectors firing when it wont start or is there no spark.
GM had a small issue with the under hood fuse box (Electrical Center), they have a circuit board in them that will sometimes crack and the under hood heat will cause random issues.
I assume there are no warning lights like the security light on the dash?

Neal

 

make sure you have a good reading and connection on your temp sensor.