The needle has just started hitting something so wont go down, have tried 4 different needles

Most likely it threw something off in the machine or locked up when the needle hit the presser foot. Unfortunately, it probably requires a service call.

look down in there there is a hook to grab the top thread may have gotten bent or loosend , you may also try comparing the new neddle with the old and be sure it is correct, look for a small latch under the grab foot, please rate -jeff

If it hit all of a sudden it most likely was your needle got bent. Replace needle and don't pull the material. Let the foot do the work.

Try installing a brand-new needle and make sure it is inserted all the way up into the needlebar. It if continues to hit, the machine quite possibly is out of time.

...

check that the selector button is fully down on the straight stitch. It should matter if the needle is straight and you have a zig zag plate on the machine. The other option is that the needle is bent and a new one may fix the problem. They dont need to be out by much but you said you had broken needles so it might even be a timing problem and hitting the bobbin case rather than taking the thread to be picked up by the racer.

If it was hitting before you stopped, it's likely that the looper either got bent or was knocked out of time. I would take it in for repair.

try another needle and see if the needle still bends,, if the needle
still does bends then there could be something wrong with the needle
bar and the machine needs to be checked.

1.replace the needle---it could be bent
2.do you have it center position for your needle setting
3.try sewing again with different fabric, if it keeps doing it then it may need adjusting by a service technican

1.needle in backwards
2.upper tension to tight
3.needle bent-try rolling the needle on a flat surface to see if it's bent or not
4.thread may be hanging on bobbin case-check for lint or fragments of old thread
5.try different thread

If the needle is not in all the way it will bottom out in the shuttle, or if you bought new needles and accedently got the wrong ones. If the needle does not enter the needle plate far enough to be bottoming out then the machine is out of time. You know i was about to hit post it and I realized I didn't think about, if the needle is bent it will hit the hook. so check those things hope it works out.