If you're having issues sharpening a knife, one (or both) of two things is probably true:
#1. Your stone isn't able to cut the steel effectively.
#2. Your stone is removing metal, but from the wrong part of the blade - if the blade has been sharpened quite a bit over the years, you may need to thin the blade in order to put a new secondary bevel on it. This may or may not be something that you want to tackle yourself - and it may be something that you want to practice on a blade that you don't mind causing some damage to, because you may need to learn some of this stuff the hard way.
Start by drawing on the side of the edge of the blade with a sharpie, and then sharpen it for 5-10 strokes. Take a look and see where the sharpie is worn off - that's where your stone is removing metal. If it's removing metal right at the edge, great - you have the right angle. If it's not removing the sharpie right at the edge, you don't have the right angle (or you may need to thin the blade in order to allow you to use the correct angle).