It is simply too dark for the camera to focus. And by default it will refuse to take the shot unless it has focused.

There are some possible workarounds: - Some cameras can be forced to take the shot when you press the button, no matter what. The inevitable result is an unsharp photo. I don't suppose that this is what you want.

• I assume that you are using the kit lens, an 18-55 f/3.5-5.6 kind of job? The downside to this type of lens is that it doesn't let in a whole lot of light, which makes the autofocus system's job more difficult. A faster lens, such as a 35mm or 50mm f/1.8 will do wonders for autofocus performance.

• Be aware that autofocus depends on focusing something that has a bit of contrast. If you point it towards a blank wall, it will most likely simply hunt and hunt and never lock on. Poor light makes this worse. Instead, point it at a part of the motive that has good contrast against the background, this will make the AF's job easier.

• Manual focus. The viewfinder of the entry-level cameras tend to be tunnel-like but you will at least get a photo this way.

• Use a flash, either the built-in one or an external one. External flashes, at least the larger models, can project a grid-pattern on to the motive to aid focusing. The built-in ones tend to strobe a number of times I think, which is not all about red-eye reduction but also helps focusing. (I am not familiar with your camera model but suspect that it does not have a separate autofocus illumination lamp and depends on the flash for this.)