I got the sewing machine.. and as you said the knob wouldn't move at all to change the stitches and they went down 75 dollars!!!!!!!!! i have cleaned it and now is working perfect! I will probably send it to be serviced tho.. I think that sewing machine has never been cleaned or serviced and I am just scared I might ruin it instead of fixing it! thank you so much for your advice!
here is the picture of my new old singer 401A I am sooo happy!