I have a craftsman 16.5 IC OHV that I just replaced the fuel cylenoid switch on because it wouldn't crank without pouring gas into carburetor. Once I changed that, it ran for about 10 minutes then shut off. I was able to jump it off with jumper cables a couple of times, and it kept shutting off. Now I can't get it started even with that. The rotor on top of the motor seems to be sticking on it. I just can even turn it with my hand. ANY ideas on what I may be able to do to loosen it up and be able to keep my lawn mower running? Thanks for any help.

The "rotor" as you called it is the "chopper" screen that is suppose to help keep debris out off the engine housing as the flywheel pulls in air to help cool the engine.
Now when trying to start and the engine stops, does it finally turn again. Or will it turn after you manually turn the "rotor" with your hand? If so, adjust your vavles. The solenoid could have a short in the wire that supplies the energy to the solenoid.

I have now changed out the starter on the engine. It still will not start. It will turn about 1 1/2 revolutions and stop again. When I try to turn it with my hand on the "chopper" it is VERY tight. If I need to loosen the valves up on it, how do I go about doing that? Thanks for any help.

Let's stay with the basics, here---check those first. Remember, very generally speaking, that engine must have fuel, it must have ignition, and it must have compression in order to run. So let's verify what we have and what we don't, first!

That you have compression is evident in that you are having (I assume) reasonable difficulty in turning (in this case) the crankshaft. Hopefully that is due to compression and not that the engine is still engaged to a load of some kind (mower blades, transmission, etc.) If the starter has sufficient energy to "crank" the engine and sounds much as it has in the past, things are likley OK there. Next, ensure that ignition is evident at the spark plug electrode during the cranking sequence---a simple task explained elsewhere here in numerous threads. Finally, I like several folks answers where they suggest supplying fuel directly to the cylinder either through the carb/air filter assembly or directly into the spark plug hole--either way is acceptable as long as a small quantity of fuel is made directly available to the combustion chamber.

Note the previous paragraph simply points you to the where the problem likley is---it does not address fixing that problem. The answer to that (we all hope) will come with your next question based on what you find!:)