I also have a Singer Simple 3116. It is my first and only machine, purchased a couple of years ago. When you turn the knob that would change from straight stitches (A) to a decorative stitch (B, C, D...) does the letter change? When my letter changes there is an audible *thump* as it locks into the next stitch. I used my zigzag (B) to stitch around some letters I fused onto a quilt the other day. I had to play with my stitch length to get it right to the way I wanted it to appear. Once, my machine wouldn't work and it was because I had the bobbin winder set to wind a bobbin and I forgot to slide it back. So when you change the stitch setting, can your machine still operate as a straight stitch? If so, then it sounds like it is the knob that is just spinning and not really catching on to switch the stitch. Hope you can figure it out!