Camera won't turn on
No matter what you do, your Nikon D610 will not power on.
Unresponsive power button
Before delving into your D610, make sure the power button is turned to the appropriate setting. Please note that even when the device is off it will sometimes still display SD card information on the screen next to the power button. If this still does not work then turn it back off and then put it back to power on.
Dead or Uncharged battery
If your D610 won't turn on, you may have simply run the battery low from over use so try charging the battery or consider purchasing a new one .
It is possible that it appears nothing is happening because the displays are possibly just incorrectly plugged in. If you feel that the device is powered on but it just is not providing visual feedback, you will need to check out the screen replacement guide.
Short circuited mother board
If the battery is fully charged and the screens have been replaced though your problem still persists then the most likely problem lies in the motherboard. If you believe that is the problem then the mother board must be replaced.
There are small, blurry spots appearing in the same spot in all of your pictures.
Dust/Oil spots on the shutter sensor lens
If small spots are consistently appearing in your pictures, there are dust particles or oil spots from the shutter collecting on the shutter sensor lens. You can fix this by wet cleaning the lens inside the camera every so often. Unfortunately this is a manufacturer design flaw and the only way to address the issue is to clean the oil spots as they appear.
Barrel and perspective distortion
Your pictures are coming out with vertical and horizontal lines being rounded, or tall structures are appearing to be leaning. This is not an issue with the camera, but a user error and Nikon provides a few techniques to reduce these image distortion types on their service website here.
Slow Autofocus during normal use
You have trouble getting the camera to focus on the object your photographing.
Test the Autofocus using a sturdy table or a Nikon approved tripod. If the problem stops then the problem was only with stabilization while using it.
Unclear Background scenery
Test the Autofocus against a different background or a focus test chart that can be found online. Mount the camera on a tripod, if the camera is able to focus on the new background or the test strip then the problem was only with the camera not being able to find an object to focus on. Try approaching the subject from a different angle, or attempt a different lens. An attempt at manual focus could be done as well. This does not fix the issue but is a good work around if the other methods don't work.
Improper Lens Calibration
If you use multiple lenses with your Nikon D610 then the problem may just be a lens calibration problem. Mount the camera on a tripod and setup a lens calibration kit a few feet away on another. Adjust the lens as needed to make the test kit clear.
Failing Focus Motor
If the problem persists the cause most likely lies in the Autofocus drive motor. If you feel this is the case you will need to remove and replace the drive motor.
The flash is either nonexistent or the amount of light produced appears to be dwindling.
Broken flash bulb
A broken flash bulb can sometimes be determined by gently shaking the camera to listen for a loose filament similar to how one would check a household light bulb. If it sounds similar to how a house bulb would sound or you can see pieces of glass moving in the flash enclosure then the flash bulb most likely needs to be replaced.
Deteriorating flash capacitor
The easiest way to check for a deteriorating flash is to ensure that the battery is above 75% and to take a few photos with flash on as quickly as possible in a dark environment. Normally the camera will prevent you from taking a photo again before the flash is fully charged with a built in timer but if the capacitor is degrading, it won’t be able to gather a charge as quickly or hold as large of a charge. If the flash degrades with each photo or the flash isn’t as bright as it used to be, then the flash capacitor needs to be replaced and requires a full teardown.
Severe Color Shift
The colors in your images are not true to the colors of the subject being photographed.
Color balance Settings
If your camera is not capturing the true colors of objects in your photos, then you can fix this problem by adjusting the color balance settings in the Selective color menu on your camera. An excellent tutorial on how to adjust these settings can be found Here.