You don't have to abandon the lens hood!!! Hoods are good a blocking the sun, eliminating solar flares AND most importantly protecting your glass.
Do this...set your camera on a tripod (or table or pile of books or anything stable) and go to your widest angle avaible to you, with the lens hood on, and shoot a picture. Then zoom in a touch and do it again. Then again and again until you have you lens zoomed all the way out.
Now, go back through your images. Somewhere within the focal range of your lens the vignetting (dark corners) will disappear. Check the first image that is clear of the hood and check your meta data for the focal length. This will give you an idea of how wide you can go without the problem.
A couple of points:
1.You may have the wrong hood for that lens. A shorter hood may work better for you.
2.Some hoods have two long flanges and two short ones. If yours does, then try placing the long flanges on the top/bottom side of the lens rather than the left/right. Because of the native aspect ration of your film plane (chip, sensor, pick a name) (i.e., it is a horizontal rectangle) the long flanges will appear at the left and right of the frame rather than the top and bottom. This is because there is less sensor to "see" the hood on the top and bottom.
Good luck...don't give up.