Couple of issues probably present.

First, the rubber paper transport bits (if they haven't been replaced) are probably hard and glazed (or squishy and sticky) by now. Reconditioning and/or replacing them could possibly restore functionality. However, since it prints a test page properly, this may not be the problem.

Second, there are probably a few paper sensor devices in there, whether they be switches or optical/contact sensors. Check around for items of this nature and test, clean, and/or replace them. Switches only have a finite number of cycles, and sensors can become clogged, carbon-tracked, or otherwise obstructed (nothing lasts forever, after all). A failure of one of these can keep an otherwise good printer down. I doubt there are a large number of any of these in the SWII, though, since it's old and relatively cheap, but there's bound to be at least one or two.