Help with melco emc6

I am looking for any kind of step by step instructions to tune up my melco emc6. I have the manuals and I have gone through the needle depth adjstments and hook timing ajust but something went wrong and now some of the needles will not come down to stitch. The ones that do still stitch will stitch for some time and then the needle bar stops coming down but the machine still running then starts again. I believe I need to make some kind of adjustment with the needle bar but I dont know what to do. It seems that the gears are not in line if that makes sence. Any help would be appreciated thanks.