My brother PE-400 sewing quit sewing

if you had a "Birds nest" when sewing, you still have some lose threads in the bobbin case and the case isn't installed correctly.

try changing the needle
try rethreading the machine top and bobbin
make sure to use every thread guide-this is improtant for the
thread tension
make sure the bobbin is turned correctly in the bobbin case
also could be a problem with the computer motherboard
or there could be a problem with the timing

You need to sew the first stitch slowly. Lower the needle by hand and take up carefully. Pull the needle thread up and the bobbin thread should be caught in the formed loop and come with it. Pull them both to the back of the machine and sew.

Try completely unthreading and rethreading it. You may also try using a different bobbin.

try a new needle
make sure the bobbin is not warped
make sure the bobbin case area is free of lint or loose thread
make sure you hold the upper thread tail while it's going down to pick up the bobbin thread
make sure there is a 2 to 4 in tail for the upper thread to grab

upper tension/threading is wrong

The "race" on your machine needs adjusting. Remove the bobbin cover, bobbin, & case. What you have left is the race, it moves when you turn the large wheel on the top right of machine. The needle also moves up and down. There is a hook on the race that catches the needle thread. Try moving the race to the line up with the needle. It may take a couple of trys but it should do the trick. Also clean any threads that may be caught on or arround the race. Hope this helps!

For embroidery, and zig-zag, and because the needle makes side movements, it needs more needle thread.
So try to keep you needle thread not very tight,
and tight up your bobbin case tension more, so that the two threads meet under the meterial.

im going to help you as much as i can,,,,try using a bobbin that is already threaded and make sure bobbin is in bobbin case correctly, make sure machine is threaded to instructions in book,,,if this is all done exactly u should not have a problem unless something is jammed

Check the timing.