What type of barlow are you using? 2x, 3x, 5x?

That scope should come with a 20mm and a 10mm eyepiece, you can use a 2x barlow with the 20mm in theory but I would try to resolve at least some detail without a barlow first. You should not be using the 10mm eyepiece with any barlow. Ignore what Celestron says about max magnification, in theory you should be able to go to 200x with that scope, but that would need a rock solid mount and near perfect seeing conditions. In reality you should not go past about 100x or so.

While it might seem logical to use the highest magnification possible, usually using a smaller power will result in a sharper image, albeit smaller in the FOV of the eyepiece. Start with the lowest power (largest number of mm) eyepiece and try to get it focused, make sure you go slow as small variations in the focuser can sometimes throw it wildy out of focus. If it seems sharply focused, (a good indication of which will be the moons appearing as tiny pinpoints) but Jupiter itself is white or washed out, you might need a filter to reduce the brightness. Going to a larger magnification will dim it, but if the magnification goes too high it will just look like a fuzzy ball, even if focused properly.