There are lots of threads on Arachnid dart machines here on this forum detailing the target head and it's troublesome switch matrix. But to boil it down to the basics:
Take target head apart and clean out the broken tips.
Wipe gunk off switch matrix and rubber damper (I use lighter fluid on a rag or paper towel).
Inspect the "segments" for cracks (particularly the pie wedge shaped ones). Replace any cracked segments as they will bind up inside the spider.
Sometimes the sealed switch matrix will go bad internally. This is an expensive item to replace (in the $100 range).