My machine is new (only used once) but now keeps jamming, appears the needle keeps jamming under the plate,please help.

Is the bobbin winder on? If so, turn it off.
Otherwise, is there power to the machine?
And this happened while you were sewing? Cut the thread above the needle eye. Rock the handwheel back and forth firmly to try to cut the thread jam below the needle plate with the sewing hook. If that doesn't work, open the bobbin case area of the machine and try to pull the bobbin case out, cutting any threads you can see with a seam ripper. Still won't come? Take the needle out of the needle clamp and throw it away (it's bent!), and take the screws out of the needle plate (=throat plate) and take the needle plate off after cutting any threads you can reach under the fabric. Keep cutting and pulling out any thread you find, and eventually, you'll be able to turn the handwheel. Clean all the thread bits, lint, and junk out of the area under the needle plate, the bobbin and bobbin case, and the shuttle area... there will be directions in your manual on how to clean the machine, including the shuttle area. Reassemble. Put in a brand new needle, right way around and fully up in the needle clamp. Rethread from scratch.
Always hold the thread ends behind the presser foot for the first couple of stitches of each seam.

See also: http://www.picturetrail.com/sfx/album/view/22521551

here is a link for parts for the sewing machine
http://www.sewingpartsonline.com/bernina-150-sewing-machine-parts.aspx

After cleaning out the bobbin area, re-threading the top thread, turning my Pfaff 4.2 off and on it still said " remove thread jam under the the stitch plate". I pushed the "ok" button and it started working again.
Keeping my fingers crossed.

try changing the needle--make sure the needle is correct for the fabric
clean under the needle plate & in the bobbin area for lint or loose threads
if it keeps jamming up & making noises I suggest to have the machine
serviced

Hello,
Here are a few things to try.

* Raise your feed dogs if your machine has this feature.

* When you start to sew a seam, hold the upper and bobbin thread tails. Hold them back and out of the way as you sew your first couple of stitches. This will keep them from getting caught in your machine.

* Your fabric may require a different needle. Generally, heavier fabrics require larger needles and thinner fabrics, smaller needles. You may also need a larger needle if you're sewing through many layers of fabric. And make sure to use a ballpoint needle for knit fabrics and a sharp needle for woven (or a universal needle for either). And make sure your needle is appropriate for the type of thread you're using.

* Adjust the pressure of your pressure foot, it may be too light for your fabric.

* If your upper thread and bobbin threads are different types, try using the same thread for both. And use a good quality, brand name thread.

* Change your needle plate. Try switching to a needle plate with a smaller hole (a straight stitch needle plate).

Important Note: If you change your needle plate, check to make sure your needle aligns perfectly with this smaller hole before starting to sew. A misaligned needle could hit the plate and break, which could be dangerous. And make sure to change your needle plate back for zigzag and other wide stitches.

I hope this helps.

Hello,
Here are several solutions to try.

- Re-thread your machine. It may be threaded incorrectly (backwards).

- Raise your feed dogs if your machine has this feature.

- When you start to sew a seam, hold the upper and bobbin thread tails. Hold them back and out of the way as you sew your first couple of stitches. This will keep them from getting caught in your machine.

- Reinsert your needle and make sure it goes all the way into the holder and that it’s positioned correctly – usually with the flat side away from the bobbin, but consult your machine’s manual to be sure.

- Change your needle, it may be blunt, bent, or otherwise damaged.

- Your fabric may require a different needle. Generally, heavier fabrics require larger needles and thinner fabrics, smaller needles. You may also need a larger needle if you’re sewing through many layers of fabric. And make sure to use a ballpoint needle for knit fabrics and a sharp needle for woven (or a universal needle for either). Make sure your needle is appropriate for the type of thread you’re using.

- Adjust the pressure of your pressure foot. It may be too light for your fabric.

- Change your thread. If your upper thread and bobbin threads are different types, try using the same thread for both. And use a good quality, brand name thread.

- Adjust your thread tension, It may be too tight or too loose.

- Change your needle plate. Try switching to a needle plate with a smaller hole (a straight stitch needle plate).

Important Note: After changing your needle plate, check to make sure your needle aligns perfectly with the smaller hole before starting to sew. A misaligned needle could hit the plate and break, which could be dangerous. And make sure to change your needle plate back for zigzag and other wide stitches.

I hope these solutions help you.

Hello,
Here are a few things to try.

* Raise your feed dogs if your machine has this feature.

* When you start to sew a seam, hold the upper and bobbin thread tails. Hold them back and out of the way as you sew your first couple of stitches. This will keep them from getting caught in your machine.



* Your fabric may require a different needle. Generally, heavier fabrics require larger needles and thinner fabrics, smaller needles. You may also need a larger needle if you’re sewing through many layers of fabric. And make sure to use a ballpoint needle for knit fabrics and a sharp needle for woven (or a universal needle for either). And make sure your needle is appropriate for the type of thread you’re using.


* Adjust the pressure of your pressure foot, it may be too light for your fabric.


* If your upper thread and bobbin threads are different types, try using the same thread for both. And use a good quality, brand name thread.



* Change your needle plate. Try switching to a needle plate with a smaller hole (a straight stitch needle plate).


Important Note: If you change your needle plate, check to make sure your needle aligns perfectly with this smaller hole before starting to sew. A misaligned needle could hit the plate and break, which could be dangerous. And make sure to change your needle plate back for zigzag and other wide stitches.

Hope this helps.

Hello,
Here are several things to try.

* When you insert your new needle, make sure it’s positioned correctly (usually with the flat side away from the bobbin, but consult your manual), that it goes all the way into the holder, and that the screw is securely tightened.


If there doesn’t seem to be a problem with your needle, try the following:

* Check your pressure foot and make sure it’s attached securely.


* Change your pressure foot Your pressure foot may be bent, causing your needle to hit it.


* Don’t sew over pins a needle that hits a pin can break. Always remove the pins from your fabric before they reach your needle.


* Don’t pull your fabric as you sew. You could be bending your needle back, causing it to hit your needle plate instead of going into the hole. Just guide your fabric, letting it feed on its own.


* Check your needle plate and make sure it's securely in position.


* Change your needle plate. If you’ve been using a straight stitch needle plate (a plate with a small hole, often used for sewing fine, delicate fabrics), switch to a needle plate with a wider hole.


* Check the position of your needle. Sewing machines with zigzag capability allow you to adjust the position of your needle – right, left, or center. If your needle is not positioned correctly, it may be hitting your needle plate or pressure foot.


* Un-thread your machine and remove your bobbin. Clean any loose thread or lint out of your
bobbin case. Re-thread your machine, reinsert and re-thread your bobbin.

* Change your bobbin. There could be a nick along the edge of your bobbin spool that’s catching your thread as you sew.

Also, before you start to sew a seam, hold the upper and bobbin thread tails. Hold them back
and out of the way as you sew your first couple of stitches. This will keep them from getting
caught in your machine.

I hope these solutions help you.

Could be the needle is the incorrect size or the thread is not compatible with the embroidery or both. :)

http://www.sewusa.com/Sewing_Machine_Instruction_Manuals.htm