When the light gets low you need to delve into slower shutter speeds than normal.
There are two different settings that may have an effect on slow shutter speeds. In normal use, the camera metering determines the shutter speed and the Menu item of Slow Shutter Limit sets the slowest automatic shutter speed that you wish to occur. The settings are 1/8 sec (the default), 1/4 sec, 1/2 sec and OFF (which is 1 second). The anti-shake mechanism works with this low shutter speed if anti-shake is turned on. It is quite possible to get shake free hand held wide angle images at 1 second exposure with a little care and a few tries.
The other slow shutter speed setting is the only manual shutter speed setting available on the camera, it's the Menu item of Time Exposure where you can choose between 1, 2, 4, or 8 seconds long exposure, and OFF of course. Take a test shot and if underexposed, change to the next slower setting etc. This is only of use with a tripod or bean bag support as the anti-shake mechanism is disabled during Time Exposure mode.
When using these long exposures by either method, always start with ISO 64. This helps to reduce image noise. If the longest exposure is still too dark, then alter the ISO to a higher setting.
Be aware that with Time Exposure selected, the shutter speeds will appear to be extended way past the 1, 2, 4 or 8 seconds chosen as black frame subtraction is automatically done to remove hot pixels caused by the CCD heatup during a long exposure.