You might have run out of space on one of the partitions. Not of disk space as such, but of file table entries - inodes.

Open a Terminal, if you have it, and try running "camera-ui". If the messages on the terminal window say something like

Timeout when requesting for resources. Going to standby
No space left on device: opening file /home/user/.omap3cam
Setting camera pipeline to running state failed.
Camera pipeline error: "Failed to configure driver module" (etc)

You have that problem and should start by getting QAD Cleaner Free and deleting some caches. That will give you a few days to read the other thread and find out which folders under /home/user/ are taking too much space and are safe to be emptied. On my case, it was /home/user/.thumbnails/