My needle holder will not hold the needle in tightly what could be causing this problem?

breaking needles from hitting can be from several problems
1-- needle /hook timing is out
2--needle thread tension is too tight pulling needle side ways
thread caught around bobbin holder is top thread too loose
take it in for a service check as the needle /hook timing is complicated to adjust and the problem could be more complicated than suggested

The needle thread breaks
1. The needle thread is not threaded properly
2. The needle thread tension is too tight
3.the needle is bent or blunt
4. The needle is incorrectly inserted into the needle holder
5. The needle thread and the bobbin thread are not set under the presser foot when starting sewing
6. The threads were not drawn to the rear after sewing
7. The thread is either too heavy or too fine for the needle
Bobbin thread breaks
1. The bobbin thread is not threaded properly in the bobbin holder
2. Lint has collected in the bobbin holder
3. The bobbin is damaged and doesn't turn smoothly

If you are pulling the arm towards you or pushing away from you then you will need to have the needle arm adjusted. Pushing and pulling of the arm will only cause damage. Many times this needs to be adjusted due to the constant movement of the machine. There is usually material on the Youtube to explain how to adjust needle arm.

if you take the serger to a sewing machine shop and show them the problem, they can check to see if the needle holder needs to be replaced or just some new screws

it sounds like the screw is stripped out or the needle holder has a problem on the left side, it would be a good idea to have the needle holder checked.

Perhaps the needle is not fully pushed in or not tight in the holder or has the needle plate moved and the needle is now hitting it? A bent needle will break as it hits the plate but apart from that I cannot imagine what is causing this.

I agree with Rick, it could be several things. It's not something a person can just start loosening screws and trying to line things up, you can do more harm then good trying to fix it yourself without the proper tools, take it to a local dealer for service!

Are you saying that the thread is breaking?

CAUSES of upper thread breaking

needle is in backwards
improperly threaded
tension to tight
needle bent or blunt
thread to coarse for size of needle
needle too long for machine
burr on needle
tension discs worn so that thread works in grove
neele too fine for size of thread and fabric
lint or dirt around bobbin case holder
irregular sewing speed
AND THE BIGGEST PROBLEM IS:
threads not properly pulled back under pressure foot when starting to sew
This means, Have enough of the upper and lower thread pulled to the back and hold for the first 2-3 stiches,

Do this every time and it will become second nature and you will do it automatically

On the side of the bobbin holder there is a spring that the thread goes under.

Holding that spring is a screw, put a couple of pieces of clothe in your machine.

Loosen the screw holding the spring 1 x 8th of a turn at a time...Until the machine sews correctly...

The needle holder has a screw right above the screw that holds the needle in place. It really doesn't look like a screw because it does not appear to have a slot for a screwdriver. However, with a small flat head screw driver you can tighten it up. There is also a curverd wire that must be inserted into a slot at the bottom of the holder. The screw tightens against the wire that tightens against the post. (It's a curved wire that curves around the front part).