Changed my battery and now my car cranks but doesn't turn over

I replaced my battery and now it doesn't start. What happened was my battery went dead so I replaced it with a new Optima battery. It started right up and ran well when I first installed it but I noticed I forgot to put these terminal protectors on, so I removed the cables, installed the protectors and reinstalled the cables. It started for a second but quickly died. I checked the connections and noticed the positive cable was slightly loose so I tightened it down and that's when the crank but no start started. I thought it might've been the protectors blocking th connection so I removed them and reinstalled the cables without them but that didn't work. Does anyone have any ideas?

UPDATE:

I decided to start from zero again by unhooking the battery, putting the terminal protectors, and seeing if draining the electric system might reset whatever went wrong. It worked for 2 key cycles but on the 3rd, it did the same thing, started up for a second and died quickly. I left it alone for a week as I had no time to work on it until today. I checked the battery and it was holding 12.5 volts non running so I decided to try again. Miraculously it started up and ran fine. I cycled the key several times and no issues. I will repost if the issue comes back up again.