Have you got the needle all the way into the holder - flat side to back? You can just see the top of the needle when it is inserted right. (Dealer gave me that hint years ago)
The other thing - take out the right needle and set it up for 3 thread stitching. Using the handwheel sew a couple of stitches. If your needle is off, bent, you will be able to spot the problem a lot easier.
Also check the stitch finger and open the cover while manually taking a stitch. If needle is hitting looper, you will see it and then get it to a dealer to fix.