Bobbon thread wont go up when I turn the knob. It was working fine and I had to change the bobbon and it wont thread

SOURCE: bobbon thread is too losse /thread breaks no

Clean out the bobbin area.

Thread the machine with the presser foot up. This opens the tension so the thread can enter. Threading with the foot down closes the tension and the thread cannot enter as it should. When you sew, the top thread is loose and cannot properly connect with the bobbin thread to form a tight stitch. The stitching does not hold and pulls right out.

Thread breakage - top thread? Check the thread spool to be sure there aren't any nicks to catch the thread.

When the thread breaks, check the spool pin to see if the thread is unwinding too fast and wrapping around the pin. Thread nets can help stop this. You can find them at sewing machine dealers.

SOURCE: how to thread cannot wind thread to pick up

What model is your sewing machine?
Linda at Relics
www.sewing-machine-manuals.com

SOURCE: bobbon thread keeps bunching

then it's very possible that the machine is out of time & needs to be serviced
make sure the needle is in serted correctly--flat side to the back of the machine & all the way up into the needle holder

SOURCE: thread keeps getting tangled in bobbon and wont sew

try changing the needle
rethread using EVERY thread guide
make sure the thread has not come off the thread take up lever
make sure the bobbin is inserted the right way--counter clockwise
make sure the bobbin case is inserted correctly if it's a side or front loading bobbin
clean in the bobbin area and under the needle plate

SOURCE: Hi. My machine sewing thread looks fine on top but gatheres at the back and wont pick up the bobbin thread. I have replaced the needle, checked the bobbon and top thread are threaded correctly.

you photo shows that the needle thread doesn't have enough tension to pull the bobbin thread up tight