I have the same exact sander and this could possibly be a simple fix and your going to need something that blows air my preferred method is an air compressor but air in a can works to. You going to want to take the dust bag off and there is a gap on the front of the sander where there are metal fins that's the area where gunk builds and all you have to do is blow compressed air into that area. The other problem could be is you covered the holes on the sanding pad with your sanding disks and that's where the sander picks up the dust. If all else fails send it to the dewalt repair center go to www.dewalt.com then go to parts and information tab now on the top right corner there is a spot that says local service center and type in your zip code.
Good luck and I hope this helps!