I saw your pictures in another thread, and it does look like that extractor rod is pretty far forward, so what DWALT suggested may well be the case. From the pictures, it appears as if the revolver is still loaded. Be very careful about where the gun is pointed, KEEP FINGER AWAY FROM TRIGGER, and give this a try:
SAFETY FIRST
1. Find a small shim, such as a business card that will fit between the frame and the bottom of the cylinder;
2. Pull back slowly and slightly on the hammer (Hammer only, not trigger, and DO NOT FULLY COCK THE GUN) until the cylinder just begins to turn. When this happens, the cylinder stop at the bottom of the frame window has dropped down, out of position.
3. Slide the shim/card stock in between the cylinder and the cylinder stop, blocking the cylinder stop from popping back up;
4. Place your left thumb on the knurled portion of the extractor rod, holding it in place;
5. With the right hand, try to turn the cylinder clockwise (as viewed from the rear of the gun), since your rod will have right-hand threads;
If the cylinder will turn, keep turning it until it stops - make sure you keep pressure on the extractor rod and it's not turning also;
6. Once the cylinder is tight, and stops turning, try opening the gun with the thumbpiece and see if it will open now.
7. If it won't turn at all, there are other methods to use, but find someone who is more familiar with S&W revolvers, such as an armorer or gunsmith and let them work on it.
8. If you can open the gun, clear it first, and then tighten the rod as tight as possible with your fingers, until you can find a gunsmith to snug it up, or come back here and someone can give you hints to tighten it better.
SAFETY FIRST
RWJ