Problems with a Craftsman 18 inch chain saw chain and clutch?

I was cutting with my chain saw when I noticed the chain really loose so I put a new sharpened chain on it and tighten it up. When I started it the engine started to bog down and the chain would barely go. I loosened the nuts and the chain started to go but fell off the bar. I did the same process over and over with the same results. I tried to move the chain to see if it free move but sometime is moved freely and others it was tight. This is without the nuts being tighten. The same with the clutch. I took the chain off and turned the clutch and it would run smoothly then get tight. Is it the chain, the way I am putting the chain on or is there something wrong with the clutch. can someone help me?