sounds like the rings are frozen to the cylinders, if they break them when it frees itself you will have serious problems. when in doubt tear into it and check the cylinders for rust etc.....when I store my car for the winter i always squirt oil in the cylinder, crank it over by hand a couple times, put plugs back in and loosen all the rocker arms, this relaxes the springs when sitting for long durations. I was lucky when i bought my car ...the original motor was rebuilt but sat for 5 years not running at all. I used a good oil in the cylinders and let it sit for a couple days....turned it easily by hand and then fired it up......lucky........if your motor is in decent shape, might just need to be reringed.....bearings might be ok.....but in the long run it will be way better to deal with a ring problem now then later on.