My D90's multiple exposure won't turn off !!

Turn the mode dial to "M". You control the shutter speed by turning the command dial, and you control the aperture by turning the aperture ring on the lens. The camera's exposure meter is shut off and won't help with the exposure. You can shoot a picture and look at it on the display to judge the exposure.

Your exposure compensation might not be set correctly. Just behind and to the right of the on/off switch you will see a small button with a "+/-" symbol. That is the exposure compensation switch. When you press it, you will see a number displayed on the LCD. If the number is positive, that is your problem. Positive numbers increase exposure and negative numbers decrease exposure. Set the compensation to 0.0 by turning the rear thumbwheel while depressing the exposure compensation button.

Could you provide some details? How does it not work? Does the D90 not turn on? Does it take a picture but the flash doesn't go off? What exposure mode(s) are you using?

It indicates "bracketing". To turn it off, press and hold the bracket button (on the front of the camera, below the flash button and above the lens release button) and turn the main command dial (on the back) to change the number of shots to 0.
Full details are in the "Exposure and Flash Bracketing" section of the manual (page 92 in my copy). If you need a manual, you can download one here. There's also a video tutorial here.

The button for this is on the right, the second one from the rear and it has multiple squares on it for a symbol. Pressing and holding this button down then turning the rear dial should change the shutter release function. It cycles through single shot, multiple shots low and high speed, and then self timer. You set the actual parameters of the self-timer from the custom setting menu.

The lens lacks the electronics to communicate with the camera. You must switch the camera to Manual exposure mode by turning the mode dial to M. The lens has only aperture, f/8, and so you have to control the exposure by changing the shutter speed and/or ISO. Unfortunately, the D90's light meter will not give you any help here.

You can get a general idea of the exposure by using another lens before mounting the 500mm. From there you can fine-tune the exposure by using the histogram display on the LCD monitor. This is how I do it with my D90 and 500mm lens.

Often, the flicker happens when the camera adjusts the exposure. The way to avoid this is to use the Manual exposure mode instead of one of the automatic modes.

Turn the mode dial to one of the PSAM modes.

Sounds like you turned on Exposure delay mode (menu d10). This is similar to the "locking up the mirror" (or somethign) feature on canons.

YOu only need it when you doing a tripod shot with long exposure and you want to minimise absolutly all possibility of shake from the camera its self. Lifting the SLR mirror will cause small shake. Generally you can turn this off (i've felt it ona few times my accident and been confused for a second)

I suggest that you try a system reset for your camera and then complete the following adjustments to see if your camera will respond like it did originally.

Nikon D90 green reset dots. Press at the same time to reset.
Nikon has an easy reset feature. I use it every time I pick up a D90.
My standard operating setting is only a few clicks different from the reset defaults.
I reset everything every time I use my camera, much as a pilot uses a checklist before every flight to prevent any switches from being in the wrong position. When I don't check first, I often have left my D90 in some screwy mode, like 2,500K WB and ISO 3,200, from shooting in the dark the night before.
My checklist is therefore Reset, Program, Basic, Medium, and A3. Allow me to explain:
1.) Reset: Hold down the +/- and AF buttons (next to the green dots) for a few seconds, and the D90 comes out of whatever crazy mode it was in and returns to sanity. The top LCD blinks and everything is back to normal.
Reset leaves the detailed menu tweaks alone and resets only the big dumb things I might have changed overnight.
Once Reset, I change these next:
2.) Program: Spin the top left exposure mode dial to P, program auto exposure.
3.) Hold QUAL and spin the rear dial until you see BASIC, and spin the front dial until you see [M]. You'll always see these on the small top LCD, and if you first tap INFO, you can see it more clearly on the huge rear LCD. (Feel free to use other settings if you have a good reason.)
4.) Hold the WB button and spin the front dial three clicks to A3. This gives warmer (more orange) photos that I prefer.

Excerpt taken from: http://www.kenrockwell.com/nikon/d90/users-guide/index.htm

Good luck and happy shooting! I have a D80 and would love to get my hands on the new D90. Make sure you also buy a quality filter for your lens UV0. The quality of the lens is just as important as the body it's attached to.

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