Make sure to check logic boards for error codes in the form of flashing LED patterns or clicking/buzzing noises...it can save a lot of time. This thought brought to you by spending way too long figuring out what why a garage door opener wouldn't go down.
#electrical
If a car new enough to have an anti-theft system isn’t starting, check that the anti-theft system is working as expected before doing any further diagnostics. Could just be that the key is dead.