Nikon D90 mirror stuck
Suddenly, while taking photos my Nikon D90 turned black and I couldn't see anything through the viewfinder, the result of a locked up mirror as I found out when taking off the lens. The camera display unit does not work either.
What can I do to fix this problem?
It may be the result of a battery going dead without prior warning. This happened to me using a third party battery pack.
In order to fix this replace the battery pack with a charged one (preferably a Nikon battery). Turning the camera on will likely result in the "Err" message being displayed. Simply press down the shutter and the mirror should move into its correct position again.
This is the problem with my battery. Is there a way to fix it or I should just replace it?