Repairing the reverse on a Husqvarna 2000 sewing machine
Husqvarna 2000, model 6440
You can find the service manual here.
and a video on this page.
Your husqvarna 2000, model 6440 machines mechanical parts are in the need for a good clean and oiling.
Most likely your reverse mechanism is stuck and needs good oiling and the old oil needs to be worked out. The best way is to take an hair dryer to warm up the reverse mechanism and even your buttonhole mechanism(You will have to take the back and front cover off for this). Or get a penetrating oil from your hardware store, normally in a spray can.
You will find that your reserve will loosen up again, but might get stuck when the it cools again. You will have to push the reverse button in and out till it releases freely. Sometimes the reverse button won't release and you need to push it back out again from the inside of the machine. Be patient, it can take a while.
Also some of the models reverse models can lock in reverse and you can lightly lift the reverse button to un-clip.
Hope this helps