Bosch 3 x 21 Belt Sander
Remove the dust bag and unplug sander for now. Everywhere you see an access hole (fan area, dust port, back of sander blow thru the tool to remove lodged dust that clogged the system, Also look for broken belt pieces in the back of sander. Then while running (remove belt) blow again thru all the ports to try and reomve as much contamination as possible. When finished you can feel to see if air coming from dust bag port, it not you still have a clog that might need more work. If I have clarified your request would you please rate this response accordingly and thank you.