Chances are the bent needle threw the timing out of whack. This is a job I would always leave to a tech professional, but there are people brave enough to work on timing themselves. I just did a quick Google search and came up with these online sources you may want to check out, but I can't vouch for any of them since I have never attempted to adjust timing myself:
https://www.youtube.com/watch?v=BT6kiYyG2bw
https://www.youtube.com/watch?v=JpVe0e009vE
http://www.ehow.com/how_12183068_adj...ming-lock.html
http://www.ehow.com/how_10005713_fix...er-serger.html
There may be others too.
Before working on the timing, one thing I would suggest is being sure to clean all of your upper tension discs. If there is just a tiny shred of thread in one of those discs (especially the right needle thread disc), that can cause the thread breaking problem. To clean, loosen the tension all the way so the tension discs separate and then use ***unwaxed*** dental floss to floss the tension discs. Also check the bottom area -- with a light and a magnifying glass, if necessary -- for any tiny stray threads that may be caught in the mechanism. For a thread you can't get out entirely, oiling can help in terms of softening up the thread to eventually make it easier to remove.