mediaslinky reply hit on the lenses, however I believe that your problem goes beyond just a lens. Fast lenses, or lenses with large apertures - f1.2, f1.4, f1.7, etc. do allow you to take in more light, however when using these apertures, your depth of field becomes very thin, and focusing (especially in the dark), is either very difficult or impossible. Manual lenses just compound the problem.
The solution for depth of field, is a smaller aperture - f8, f11, etc. however this is the opposite of a fast lens. So you are back to needing to gather additional light, flash, turning on lamps in the room, or leaving the shutter open for a longer time, and/or increasing the sensor's sensitivity (higher ISO speed).
You can do all of this with your current lens. Increase the ISO speed to your camera's maximum value (if the room is as dark as you indicate). Increase the shutter time to 30 seconds and beyond. For this you probably need a tripod, and remote shutter release (wired or IR).
If your setting is something like a very dark night club, then a body like the K5, with very high ISO and a focus assist light. However, even with a fast lens say at f1.7 your depth of field will be pretty thing, and focusing will be critical.
If you go to faster ISO speeds, you will probably need noise reduction utilities to clean the images up a bit.
Overall, you need to provide a bit more information with what your are trying to do...