I had this problem myself. Things that may break the adaptor are listed below.
1) physical damage. As in tossing it, kicked, dropped repeatedly and from high places.
2) water damage. Dropped in toilet, puddles, pools, etc.
3) neglect. If you don't use it, you lose it.
4) electrical damage. If it was plugged in the device when the device dies or charging, it has the high chance of going caput.
These are the main causes for the wireless adaptor not working. I recommend switching to a regular DS/DS lite, which has internal wireless or getting another adaptor off of amazon.