Well, that's really weird have you tried clearing the cache and the data of the Gallery application, if not then try doing it by going to the task manager> Gallery, clear the data and the cache. Once done again try opening the gallery and check if you can view the previews of the taken photos and ..... !! If that still doesn't helps you then try factory resetting your device.
Otherwise what you can do is wait a bit unless some other Admins, Moderator, or members come out with some new trick. I hope clearing cache and data will work out for you.
PS: Before factory resetting always remember to backup you data before moving forward as factory resetting will make remove all the personnel data.