Empty the dust and dirt collection container on your Shark bagless vacuum cleaner. If this container (accessible from the rear of the vacuum) fills up, it could prevent the vacuum from sucking up any additional debris off the floor.
Change your filters. Shark bagless vacuum cleaner models have a variety of filters installed, including a dust cup filter, a secondary filter and a motor filter. If any of these filters become clogged or need cleaning, your vacuum cleaner may lose its sucking power.
Verify that nothing is lodged in the bottom of your vacuum and that the bristles that make contact with the floor are still spinning. As you move your vacuum across your floor, a brush underneath the base helps dislodge and suck up debris. If you try to suck up something that is too large for the vacuum, these bristles may get stuck and stop spinning, preventing the vacuum from effectively removing dirt and dust from the floor.