I have bought & using Brother BM2600 two months ago. Now when I sew, it's very slow or the machine just "hrrrrr" and doesn't run at all. like the machine is very tight and doesn't run properly. When I used the handwheel I can feel that it doesn't turn normal. Its hard to rotate. But if I use the bobbin winder, its running okay.

That's far too little time to be needing lubricated.

It wasn't by chance dropped or anything?