I hate the "everything was working fine and now it's not working" stuff.
When you say the threads don't connect, does one or the other thread travel/look like it is stitching and pulls along, or does one or the other stay short?
First thing is deep breaths. Reclean and reset the bobbin, looking for little tiny bits of fuzz. Test. If still not working, time to rethread the top, following the manual. Sometimes a thread will jump or loop out of place. Also, put in a fresh needle -- even new needles can have problems any they are much cheaper than our time or aggravation!
Good luck and welcome to the boards. You can do this!!
Also, do you pull your thread up from the bobbin case? Some machines are fussier about this than others.