First, check the blue wire that connects from the headshell to the cartridge pin, it's probably loose or off. If you need to tighten it, put a tooth pick inside and tighten with a pliers. The toothpick will keep it from totally collapsing.
If this is not the problem check the left tonarm cable where it plugs into the back of the preamp/phono stage make sure that the outer ring is tight and making good contact.
If that doesn't work, you may want to take out your arm cable, where it plugs into the bottom of the arm and reseat it.
If this is not the problem check the left tonarm cable where it plugs into the back of the preamp/phono stage make sure that the outer ring is tight and making good contact.
If that doesn't work, you may want to take out your arm cable, where it plugs into the bottom of the arm and reseat it.