2005 Mazda 3 Main Fuse Box

Engine Mechanical problem
2005 Mazda 3 4 cyl Two Wheel Drive Manual

My car was fine until yesterday when it would not start. When I tried to start the car, the radio, lights, air conditioner, etc. Worked, so I wasn't sure if the battery was dead. Anyway, I did jump start the car, and it is running again, but the check engine light is on. Here is the strange thing: When I popped the hood to give the car a jump, I noticed that on the driver's side, to the right of the battery, where the owner's manual tells me I should find the main fuse box, there is a recessed area, with a piece of velcro and a black wire with a blue connector just dangling loose. Did someone steal my main fuse box? I noticed that one of my hubcaps had been stolen, so perhaps something from under the hood was taken as well. Is it possible that my main fuse box was stolen, and if it was, what effect would that have on my car? Could that explain why it would not start and why the check engine light is now on?