My Bernina 801 suddenly stopped pulling the fabric thru unless I push down on the stitch-length selector knob. If I don't hold the knob down, it will only sew in one spot. What do I do I fix it??

SOURCE: sewing backwards

The reverse button works by hitting it twice in succession to make it stay on (it lights up), and you turn it off my hitting it once again. If you just want to reverse for a little bit, you hold it down while you sew, then let go. Is the button lit all the time?
Having said that, it sounds like Nannayoyo needs to take her machine to a service centre - the electronics behind the button panel might need replacing. Is it possible the button is stuck in? Maybe phone a Husqvarna service person - not a sales person - and ask for advice.
Everyone - are your machines new? If yes, you need to go back to the sales centre straight away and get it fixed or replaced while you wait. If these are problems that have just appeared when your machine used to work perfectly, probably the best solution is to take it for a service. It might just be a speck of dust has settled on the electronics behind the panel and is causing unpredictable behaviour.

SOURCE: reverse sewing button stuck HELP!!

MOdel 6430 has the stitch length and buttonhole selector on the same knob. It is the one on the bottom right side of the machine. I believe you may have selected the buttonhole by pulling out on the large round knob. You need to turn the knob back to 0 zero and push in. This should return the machine to normal mode.Adjust your stitch length to 3 and try it. The reverse knob in the center should also stick out so that it becomes operational again.
sewman7

SOURCE: Bernina 1630 problem

Your feed dogs sound like they are getting stuck,chec whether they are on the down position,and also make sure that you have cleaned any lint that builds up in the bobbin area, if all fails it will have to go into the technician,

SOURCE: Bernina 440 stops stitching

see your local dealer and tell them you have a bad power board. or l-print. this is a known issue and bernina is covering it under there 5 year warranty. the 5 volt output is faulty on some some models

SOURCE: Singer Touch Tronic 2001 Sewing Machine Stuck on Sewing Straight Stitch Only

I had a similar problem a couple of years ago. I finally figured out that I had the straight stitch needle plate (the one with the single hole), rather than the zig zag needle plate (the one with the curved hole). When I changed plates, it worked fine.