Canon IXUS 850IS manual mode

Sounds like you need longer ex[posures, not shorter. In either case, you are out of luck since the 850IS doesn't let you alter the shutter or aperture settings. The so called "manual" mode only lets you apply exposure compensation, correct colour and change white balance. Photos that are too dark are underexposed (not enough light reached the sensor) which means the shutter was not open long enough, or the aperture was not wide enough. On the 850IS you can use exposure compensation to add extra stops (more exposure). If you can change the ISO to a higher number, this will also help, but at the cost of "noisier" images. As to the anti-shake not working; it probably is, but at very low shutter speeds, it is not enough - get a tripod or at least place the camera on a very firm support. A bean bag is excellent for this, becuse it moulds to the surface and to the camera, helps keep the camera from moving and protects the camera body from damage at the same time.