Are you having problems with your thread frying or looping on the bottom of you fabric? Take you presser foot off and look to see if your needle plate looks like this. See the sharp points in the middle of the needle plate hole.  This is common for people who sew heavy seems or those of you who like to pull you fabric through and not let the feed dogs do the work.  What happens is the needle flexes and hits the edge of your plate and will cause this burr and as a result the thread in your needle goes down too hook the bobbin thread and gets caught on the sharp edge and causes you the frustration.

So take the needle plate off your machine and lets bet rid of these sharp edges.  You can sacrifice your Popsicle style finger nail file and crack it in half the long way.  Now you can file the sharp edges off in the hole the best you can.  Sand paper will work but it doesn’t hold up as well.  Really all you need is to get the sharp burrs knocked down.  At some point you will need to have the plate addressed but this should get you by until you can file and polish these out.

Good luck!