Low light with auto-focus

It will help to know what camera, but sounds like it is hooped.

The reason the camera has the green light is not to warn that the flash is off. The green light is used to help the camera auto-focus in low light situations. If you disable auto-focus and use manual focus the green light should not flash when taking the picture. Let me know if that helps!

Sounds like the auto focus is not keeping up.
There are situations where auto focus should not be used and the manual override the preferred method. Low light and single colour subjects are high on the list.

If you have a filter on the camera try removing it.

It sounds like you are either too close to the subject or you need to flip the focus switch to automatic.
The Auto/Manual focus button is located on the left side of the camcorder under the LCD monitor flap.
Other than that, does this happen only in low light? The camera will have trouble focusing in low light usually.

The 510 seems to have trouble auto-focusing in low light. Manual focus works if there is enough light for your eyes.

The Nikon D100 custom settings option 22 - AF Assist, controls the AF Assist light.
Check if this has been turned off.

This option controls whether the auto-focus assist light comes on in low light to help autofocus
latch onto the subject.

in low light or low contrast situations, the camera will not focus...press the [---] and change the point to center focus and increase the iso

This is the camera trying to give itself enough light to focus with.

As it uses contrast to focus with you will get problems in low light conditions. There's no way round this I'm afraid except to light the subject better. As it's a digital camera and you're not wasting film, try manual focus and see what results you get.

Way to check settings is to take the batteries out for a while, it should revert to factory default settings. I tell a lot of People to try this, it works an amazing number of times. Auto focus looks for vertical lines, what are You shooting at? Try rotating the camera 90 degrees, if it locks better,Bingo. Subjects without much contrast are hard to lock focus on

Without seeing a photo, here are a few possibilities. 1) Shutter speed too low (camera shake). 2) Camera is focusing on something in the foreground. 3) Focus not locked, low light, low contrast scene. Items 2 and 3 can be corrected by manual focus. Set the focus to 1 click below infinity, depth of field will insure everything is in focus. For item 1 remember that the shutter speed must be 1/125 sec or faster at full zoom to avoid camera shake.