I have a Brother SE-400 where the needle bar is completely seized. I was sewing, ran over a pin, and my machine just stopped. The wheel would not turn at all. I removed the plastic case and loosened the set screw on the needle bar crank rod from the needle bar and everything moves freely, except I am unable to move the needle bar - even with the crank rod disconnected.

Sewing Machines - Brother - SE400 Computerized Sewing Machine