Starting problems

I just got a 92 Isuzu pickup. I tried starting it up, it turned over n ran a minute. I turned it off then tried it again and all I get is click click click. Pulled the starter an had it checked but it was fine. Got a new starter to make sure, same thing started, turned it off then tried it again and click click click. Not a mechanic so not sure what it is. We even checked the fly wheel to make sure there was no bad spots on it. Plus it ain't the battery. I don't know what the hell is the problem. Any help would be cool. I don't wanna spend hella to a mechanic to find out it was somethin easy I could do. Thanks in advance.