Serger is threaded correctly, added new needle, threads do not form on stitch finger to connect to fabric when sewing. What's up?

I don't know your model in particular but generally this is how you set up a serger/overlocker to create a rolled hem. Remove the left hand needle and thread if 4 threads are threaded). Now there is usually a lever around the stitching area that you slide back towards you to remove the stitching finger back (disengaged). Then you adjust the top looper tension looser (about 2-3) and lower looper tension tighter (7 or 8). Leave needle tension at normal tension (5). You may need to move the cutting blade to the right too. The technique is to cut the fabric wider but with a narrow stitch so the cut edge rolls under within the stitching. You want the top looper thread really loose so it rolls right around underneath up against the needle thread, the lower looper thread needs to be tight and almost invisible, pulling the upper looper thread down. I usually do a few test runs and check the stitching. Once happy, I turn the stitch length right down to 1 so it is very dense. This uses a lot of thread up.

Ideally use a wooly overlock thread on the upper looper as this "fluffs" out once stitched and "fills" in covering the fabric edge completely.
some good images here
Sewing Basics Narrow Rolled Hems with Serger Sew Mama Sew Outstanding...

Hello

The serger chain will wrap or stack around the stitch fingers when stitching without fabric, this is normal. Place two layers of medium weight woven cotton under the presser foot and begin serging, the chain will wrap around the fabric cut edge to form stitches and 'push off' the originally stacked stitches.

Happy Serging
Sewingirl/

SKIPPED STITCHES ON A SERGER

1. Is the needle bent or worn--replace

2. Is the needle inserted correctly into the needle holder--check needle

3. Is the Serger threaded correctly--rethread

4. Is the presser foot pressure right for the fabric--adjust
5. are the needles the correct ones for the serger
6. Possible timing problem--need to be checked at a sewing machine shop

try changing the needle--make sure the needle is the correct one
for the fabric being sewed.
also make sure the needle is turned the correct way in the needle
holder and pushed all the way up into the needle holder.

try changing the needles--make sure the needle are the correct
one for the fabric being sewed
make sure the machine is threaded correctly
this link has parts for the serger and a manual
http://www.sewingpartsonline.com/janome-434D-sewing-machine-parts.aspx

is it possible that the needles are in backwards?
it's very possible that the machine is out of time & would have to be taken to a sewing machine repair shop to be retimed

Lower the pressure on the feed dogs, use a stretch stitch, and longer stitch length. Be sure to use a good quality thread, and maybe go lighter weight thread.

You 910 serger doesn't have the option for a Chain Stitch. It is a 2, 3, or 4 thread serger. You can do a good number of different stitches but a chain stich is not one of them.

If what you mean it that it won't "chain off", meaning sew with no fabric beneath the foot as you gently pull the thread towards the rear of the machine, that could be for a number of different reasons. First, change the needles and unthread the machine and start over. If the threads are not exactly where they should be, your serger won't sew correctly. A great video on threading your machine can be seen at:http://www.husqvarnaviking.com/mediafiles/huskylock/index_en.html

The loopers must be threaded before the needles.

Make sure that the needles are not threaded. Thread the loopers and have the loose ends behind the presser foot. Then re-thread the needles and place a scrap of fabric under the foot and sew. Make sure that the edge of the fabric is not to the right of the plate, but where it would be if the knife had cut it.