It's only with manual mode that you're having this issue?[br]
[br]
If it is, are you sure that you're that you have the aperture, shutter speed, and ISO set correctly for proper exposure? When you're taking a photo, look at the exposure level indicator to check (the scale on the screen that goes from -3 to +3). Underneath the scale should be a vertical bar which shows you the exposure level. Ideally, the bar should be close to 0. If the bar is all the way to the left by the -3, then the camera is just not getting enough light. If that's the case, you need to lower the aperture, lower the shutter speed, or increase the ISO until the bar is closer to the 0 on the exposure level indicator.