motor wont turn over?

I put the motor together myself about 2 years ago, It's is very clean inside, I just had the heads off. it sat, inside for about a year. that's why I pulled the heads, just to check it out. so I put new head gaskets on it and put it all back together. it turns over quick without the plugs in it, when I put the plugs in it it will barely bump over, you can hear the starter trying to turn, but wont