I assume it is not turning over based on your description. So go with the battery basics first. Make sure your connections are tight with no corrosion. Next make sure the battery has enough power. If you have sufficient power it might be the VATS which you can bypass, or what Tyler suggested it is. If it is turning over but not starting then go through the fuel basics.
Let us know how you are progressing so we can help you to figure it out.
