Wrenkins what sort of mess is your overlocker making? Is it the thread or when the blade is cutting is it leaving a mess that the overlocking doesn't cover?
The lower blade can get blunt and will need changing and sometimes the manufacturers include a spare blade in the pack with all the bits and bobs that comes with a new machine, i.e. net covers for cones, tweezers, screw drivers etc.
So back to your problem, if necessary re thread properly the overlocker and if you can use different colours so you can see what they are doing, and then compare your stitching with that in your manual and hopefully you will see if one of the colours is out of line, i.e. not stitching properly.
When a thread breaks, often we think the quickest and easiest way is just to rethread that particular thread, and unfortunately that is not the case, you should really unthread everything and start threading with the upper looper, then the lower looper and then the needle/needles - that way they are laying in the right place particularly up near the blades. Also where the thread goes through the tension discs, if you put one hand behind and one hand in front of the tension discs give the thread a little tug and this should settle the thread in the discs properly. Make sure that the spools of thread are flowing off the pins at the back and up through the rod that holds the feed. If thread is falling off the spool use the nets supplied to stop this. Also in the pack of accessories you have there should be some little flatish spool caps so try using these as it makes the thread coming off the spool feed properly. Also without thread in the tension discs take a piece of dental floss and work between the discs - it is surprising just how much dust and muck can get in there and the floss should help clean this out. Also clean the dust and debris away from the blades and all around and oil regularly especially where it indicates this on your manual. When you think about it the machine runs so very fast it needs to be kept clear of fluff and debris and it needs oiling.
If none of the above help then it is possible that the lower blade is the problem and yes they can become blunt - it all depends on just how much the machine has been used and exactly what fabric it has been cutting.
I hope that by following the above you can identify what is wrong, fingers crossed that you haven't done some damage by hitting that pin, also listen to the machine and see if it is sounding different - part of the pin could have dropped down into the mechanism and then I am afraid it is off to the repair place.
Now back to Acorn, I really didn't mean to scare you about pins, it was seeing a pin in your work that made me post about the damage pins can cause and as others have said they have hit a pin some have got away with it and others haven't. As you are such a newbie to an overlocker there is time for you to start with good habits. Don't be put off though.