Easy DIY Home Decor Crafts: Drywall disasters

I think I need some professional help on fixing my drywall / ceilings in preparation to paint. I've tried fixing the cracks above the door openings in the past with everything from spackle to the "elastic" type that is supposed to keep the cracks from re-appearing. They always do reappear. I had some foundation issues that I *think* are fixed, but after "fixing," the nail pops appeared in the ceiling.
Then there are the corner or edge issues that I've tried to fix, but they end up cracking, too, and pretty soon, somebody comes by and says "Hey, did you see that this is cracking off?" and proceeds to pop off the cracked bits. :-/
Then there are the issues of the ceiling separating from the walls that were structurally fixed (the builders didn't attach the ceiling joists to the wall joists, so during the winter, when the ceiling joists shrink, up goes the ceiling), but now I don't know how to fix the mess of the drywall. While fixing the rising ceilings, one of the guys slipped and almost come through the ceiling... and I have no idea how to fix what I call the "splat" ceilings without it looking OBVIOUSLY patched.
All comments welcome, but I'm leaning toward needing a reputable drywall person come fix all of the above.