My best guess is that the rocker stud (under the valve cover) has backed out of the head and now 1 valve is working. Remove the valve cover and have a look. There are lots of resources on the web for adjusting the valve lash on your engine. Excessive gap on the intake valve will not allow the compression release to function- so then you get a hard to crank over condition. If the stud did in fact loosen up, loctite it back in w/ red. You will want to know that the pushrod is straight and that 2 small valve stem caps are still there.