Nikon D300, purchased 14 months ago. Pictures are not as clear.

Appears that the auto focus mechanism is not working, This anomaly is most obvious in lower light situations when focusing is much more critical.

If the camera was new and two months old I would either return it for another one or have Nikon repair the lens assembly under the terms of its warranty.

No. The D60's LCD is used for menus, shooting settings, and reviewing pictures after you take them. You have to use the viewfinder to compose your pictures. Nikon introduced the LiveView capability into their DSLRs with the D3 and the D300, introduced after the D60.

The D40 works as SLRs have worked for half a century, showing the view only through the viewfinder. The LCD is for menus, setup, and reviewing pictures you've already taken. The LiveView capability that allows you to use the LCD for composing your pictures is a relatively new feature. Nikon introduced it into their cameras with the D3 and D300, released well after the D40.

Sorry if that wasn't the answer you wanted to see, but that's the way this camera works.

its the aperture, the ring must be LOCKED. sometimes it may be dirt, so clean contacts and turn the ring to f22 and lock.

Set the ISO as high as it will go and the aperture as low as possible. That is as good as it gets without investing a lot of money in pro cameras and lenses that are needed to shoot action in low light. I have a D300 and a 70-200mm f2.8 lens that together cost almost $4000 and it can barely do it. How bad do you want pictures?

I have had "dark pictures" from each of my Nikon DSLR (D70, D80, D200, D300) cameras usually when taking pictures from a tripod and/or the self timer. Situations where you take your eye away from the viewfinder which allows stray light to enter thru the viewfinder and throw the auto exposure way off. Not sure if this is what is happening to you.

are you using mirror lock-up or live-view feature?

send it back to NIkon..

Im not trying to sound degrading, but isnt there a little button on the bottom right of the display that turns it on or off? I know there is on the D70 and D80, Ive never actually used a D300 myself, bu tI just thought maybe thay had a common trait.

Other than that, can you still use the rest of the camera, like taking pictures and whatnot?

Take the lens off and put it back on the camera again. Make sure you turn the camera off prior to doing this. Make sure your lens is at it's smallest aperture setting.