I have a Nikon D3100. It doesn't take pictures while the built in flash is popped up, but is working fine when the flash is down. What could be causing this?
2In what mode? All automatic or Aperture/Speed priority?– xenoidFeb 18 at 10:55
I'm guessing that the exposure settings are significantly different (darker) when the flash is up because it is expecting the flash to add a lot of light. If the exposure settings are dark enough that the camera cannot achieve/verify focus it will not take a picture (except when set to manual focus).
Alternatively, if the camera is set to the continuous release mode it will not take a picture when the popup flash is enabled... the two functions are incompatible (pg 53 of the manual).