96 Trooper cranks but won't start...

My mistake.... :-o

When I first got the trooper it ran fine and then all of a sudden at times when I turned the key it would do absolutley nothing and I could wait awhile and then turn the key and it would start. Then it started loosing power and getting alot of hesitation. Now, I turn the key and it cranks but won't start up at all. I've replaced the spark plugs and air filter so far but the problem still exists (turns over but won't start). Any ideas? If there's something more I can check myself, I would rather do that instead of handing out lot's of $ that I don't really have. Thank You...