Lens elements upset

There are a series of small brass "buttons" on the outside bottom of the lens where contact is established. If a new lens, there may be some dirt or grease on them preventing contack. Wipe lens and camera buttons carefully with a lent free cloth and retry. Then it is time to go back to the seller.

Don't even think of disassembling it yourself!!!!!! Take it to a professional camera repair man and save yourself allot of money. I guarantee you that if you disassemble it yourself, you will not be able to reassemble it and the repair man will charge you much more then if you just brought him the lens in the first place.

Why do you think that the lens needs to be internally cleaned in the first place? It is very rare for so much dirt to penetrate the lens's interior that it actually affects the quality of the photographs. Don't over react to a few specks of dust between elements. The most important element to keep clean is the exterior surface of the rear element because that is where the light is most concentrated. Let a camera repair man tell you if your lens really needs such a drastic approach.

I hope there is no mild on the lens, because that is irreparable. When you look in the lens barrel, and you see an element with a tray haze over its surface, there is a chance it has mould on the element. Making the lens unusable.

Could be several reasons. The front lens is dirty. That can be cleaned with a lens pen. Or a soft cloth, the same as you should use for your glasses.
It could be there is mould in the lens system. You can see this when looking into the lens, passed the front lens. That can't be fixed, without replacing the whole lens.
And when the camera is dropped on the lens, it could be the elements are not aligned anymore. Same as with mould, only an expensive repair could cure that.
I hope you did not try to clean the front lens with any fluid like alcohol, because that is irreparable to.

If you realy have fungus in your zoom lens, you can't do anything. If it does not show on the pictures, just keep the lens dry. (use silica gel) If you want it it be repaired, it will cost more than an new lens.

Hi,IF I were you I will search the eBay for a same lens as " parts only " which means lens does not work but you can use the some parts of it ..There are a lot on ebay..one example is below URL..pls visit both..
Brand name services always do this..Since you were doing unauthorized repair ,they do not like it..
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Item condition:For parts or not working

http://cgi.ebay.com/Nikon-Nikkor-18-200mm-ED-AF-S-3-5-5-6-READ-/200635517251?pt=Camera_Lenses&hash=item2eb6cf0943
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parts;
http://photography.shop.ebay.com/Lenses-/3323/i.html?_kw=Nikon&_kw=parts&_dmpt=Camera_Lenses&_stpos=&gbr=1

Okay. I just wanted to scare you away from ruining a perfectly good (or nearly so) lens, but a learning project is a different matter. And a lens collimator is not that hard to build. One source is the book "Camera Maintenance & Repair" by Thomas Tomosy. I'm sure a quick Google search would show even more.

I did the same thing myself decades ago, taking apart a damaged zoom lens. Unfortunately, I never got it working properly again :-( But it was an educational experience, even though I didn't have a lens collimator...

This is actually a very common situation for older lenses. You should take the lens to a trained technician and have them clean the inner elements of the lens. Often times they can, if the fungus isn't too bad. In extreme situations, they will need to replace the element itself.

The fading (flare) you see could simply be a finger smudge or other stuff. One little scratch won't do it, you'd have to take sandpaper to the lens to see obvious flare.

It's actually harder to scratch a modern lens than most people think. When it happens, it's usually during cleaning when a tiny piece of grit is on the surface and gets rubbed in by the cleaning cloth/lens tissue.

So the first step in cleaning a lens surface is to be sure you remove all dust and dirt without rubbing. The lens cleaning kit you can find in any camera store is a start -- it contains a blower brush. With the lens surface to be cleaned facing down (so dust falls away), brush gently with the tips of the bristles to dislodge stuff. Then use the blower to blow it away. Repeat as needed.

If you still see dust and dirt which seems to be stuck on the surface, take a piece of the lens tissue from the kit and put several drops of the cleaning solution on it, enough to get it pretty damp. (Always apply cleaning solution to the tissue or cloth, never drop directly on the lens surface.) Cover the lens surface with the damp tissue, pressing it into the corners, but do not slide the tissue across the surface. Just lift it away. Repeat with another section of tissue.

Then take a full sheet, wad it lightly, and wet it. You are going to rub lightly, using a roll-up motion as you move the tissue so that dust/dirt is lifted away from the surface and fresh tissue is always coming in contact with the surface. Repeat as needed until there isn't any visible stuff.

Final cleaning can be done with a fresh piece of tissue and a bit of mist from your breath. Mist the surface, and lightly polish with the tissue to remove any remaining cleaner residue.

Its more like a distorted inner zoom barrel or sand and dirt inside  the inner barrel will need to be replaced or you need to dismantle and clean out