I am not an expert on these matters, but it sounds to me like your optical system is badly in need of being collimated. In a well-collimated system, the center of the mirror is on the same line as the center of the secondary mirror, the correcting lens and the eyepiece. If these elements are off-axis, you can get all sorts of non-optimal images. Usually stars look like fuzzy comets, an effect called 'coma'. Your primary mirror orientation should be adjustable by turning a set of 3 screws at the back of the mirror cell.
To collimate the optics, point the telescope at a distant light source and look through the telescope with the eyepiece out. You should see a set of concentric images of the primary mirror, the secondary mirror, and in the middle, the distant light source. You need to tweak the orientation of the primary until you get this to happen. Alternately, by trial and error, look at a bright star or planet through the eyepiece at low power, and adjust the mirror until the image quality improves.
Sorry I can't be more specific. Another problem might be the reflectivity of the mirrors. Open the telescope up and inspect the primary and secondary mirrors for tarnish. Re-coating bad mirrors might help the image brightness, but fuzzy images are a product of bad collimation usually.