After interference, the needle won't reposition left or right properly.

A few things you can check are.

1. is the needle the right one for the machine?
2. is the needle properly inserted and oriented correctly for the machine?
3. Is the bobbin inserted correctly, so it unspools correctly for the machine?

If that all looks right, then take the needle plate off and watch the shuttle hook. It should be very close to the needle when the needle is at its bottom most part of the stroke. If it is well behind, your machine\'s timing is retarded. You\'ll need to take it in for adjustment.

I looked through an online copy of your instruction manual and I don't see a guide which says what that symbol means. To me it means that the upper thread isn't threaded properly. Try one more time to rethread the upper thread but make sure your pressure foot is in the UP position. You may also want to use a piece of unwaxed dental floss and see if you can clean between the tension discs.

I went to Singer for you and found this bit of "help" Perhaps this will help you get back to sewing. It's worth a try.

"
You may have accidentally lowered the buttonhole lever located just to the left of the needle bar. To make sure it is in the correct position for sewing, place your finger under the lever and push up.
Also make sure the needle is set at the highest position and the bobbin winding spindle has been pushed back to the left or the machine will keep beeping every time you try to sew.
NOTE: To set the needle at the highest position, turn the hand wheel TOWARDS you, until the needle moves to the highest position. Finally, push the reverse button a couple of times, this will reset the machine.
If none of the troubleshooting techniques above solved the issue, please contact a SINGER Service Center to have your machine serviced."

Good luck

SKIPPED STITCHES
1.the needle is not inserted correctly
2.the needle is damaged
3.the wrong size needle is being used
4.the foot is not attached correctly

the machine may need to be serviced to see why the needle position won't
move

Make sure, Joe, that your needles are pushed up into needle bar shaft a's high a's they will go. Although same length, the left needle will appear higher than the one on right side when properly seated and tighten clamp screw securely. Check Lower Looper for proper threading--thread delivery eye of lower looper to far left "hidden" from sight. Use looper tweezers and it helps threading it. The thread then gets pulled to right side and goes front to back of that hole in front of you on lower looper. Follow threading guide on the cover door to right of your serger. Hope this helps. Jimmy

have you checked the needle to see if it's damaged,,if not sure replace the needle--flat side to the back side of the machine--all the way up into the needle holder
is it possible that you wound a bobbin & the bobbin winder spindle was not returned to the left position

have you checked the needle to make sure it's in correctly--flat side of needle goes to the back of the machine

correct needle insertion is mandatory for the proper use in your sewing machine. Raise the needle bar to the highest point, then loosen the needle clamp screw to remove the old needle.
place the new needle in the needle clamp with the flat side of the needle facing the back (or if using a round needle the groove in the needle should be facing away from the shaft.
push the needle all the way up to the stop, or as far as it will go, then tighten the needle clamp screw.

how to decide which needle is correct to sew with, it depends on the fabric & thread being used for the project.
like for example, I've been sewing for over 30 years, I'm sewing a stretchy fabric & regular needles won't work because they skip stitches & will pull the fabric thus damaging the fabric, the needle I have to use is a singer universal ball point needles, & I have no problem with the stitches they come out fine.

If you can't turn the handwheel, then there is thread jamed up in the hook. You can try to rock the handwheel back and forth to try to get the thread out. If you do get it free, try to sew with it. If it won't sew properly you might have a damaged position finger or it's out of time. You'll need to take it to a PFAFF dealer.

I had that problem too! I usually turn the tension knob and it works,