Nikon D90 the mirror is locked half way. I can see half the picute and camera shutter works okay

I'm going to assume at this point that the camera has been serviced correctly. What I'd suggest is that you look in your manual and find where you can reset your camera back to the factory default settings. Okay here are a few thoughts that might be what is happening again I'm assuming the service was done correctly. In "Auto" mode the camera is in full control and what might be happening is the camera has selected a shutter speed many seconds long to achieve a correct exposure, most DSLR's will have a 30 second shutter speed. Also the mirror up function my be activated so first the mirror comes up then the shutter delay happens. The mirror lock up function on my fleet of digital cameras locks up every time I trip the shutter until I set the function to off. It'll really throw you off if the mirror lock up is activated, the camera is set for a time delay be this 5 or 10 seconds and then you have a long exposure on top of that, feels like forever before the picture is actually taken. By going into your setting or custom functions and setting the the camera back to factory default so bring you back to the setting the camera had when you first got it.

This may be the shutter but it's more likely a common issue where the secondary mirror does not fully lift and leaves a shadow on the sensor.

Either way, whether it's the mirror or the shutter, you cannot repair these faults. Your camera should still be under Nikon's warranty, so you should send it to them for a free repair. Note that any unauthorised attempt to fix these issues invalidates the warranty.

Sorry there's no quick fix for you, but I hope that my reply has still been informative and useful. Please take a moment to rate my answer.

You have auto-bracketing on. It's the little button labled "bkt" by the D90 logo in the front.

Having gone over a month without a response, I assume this is no longer a problem.

Your mirror is not fully opening, make sure you have no dust or object jamming the mirror. Do a cleaning with the mirror locked up in the raised position.

You "release the shutter" by pressing the shutter release button, often called the shutter button. That's the button you press to take a picture :-)

The camera may or may not return to normal after that. If it doesn't, remove the battery, then put it back in and turn the camera on again. Try removing and reattaching the lens (with the power off). If the problem persists, have a certified Nikon tech look at it.

Try pressing and releasing the shutter button. If that doesn't do anything, then turn the camera off and on and press and release the shutter button. If that still doesn't do anything, then turn the camera off, remove and reinsert the batteries (or a fresh set, if readily available), turn the camera on, and press and release the shutter button.

I ran across a Nikon N80 last week which hadn't been used for many moons. I tried the shutter and the mirror promptly locked up. It took about half a dozen tries, but the mirror eventually shook loose or whatever, and the camera now works perfectly.

If the above procedure doesn't do it, then you may have to take it in to a good camera shop for a CLA (clean-lubricate-adjust), the camera equivalent of an automobile tune-up.

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)

bring it to your nearest nikon shop for a check up. i suggest a mirror lock up / shutter error.

There is an almost certainty that your mirror and shutter is going to experience problems in the future. Any fall of that nature is SURE to jar the shutter and the mirror very badly. The shutter is probably damaged already. Go out in the bright sun and shoot on shutter priority at the highest shutter speed (I think the 90 is 4000 /s?) and see if the shutter makes a stuttering noise...Also go into your menu and set the mirror to "Lock up" (for cleaning purposes), if both of these things work ok, you should be ok for a while. But do not depend on the camera for anything really important such as weddings unless you have a backup camera...