The Nintendo DS is the most popular portable gaming device on the market. As a result, there is no shortage of people reporting problems with either the software or hardware for the DS. Thankfully, with so many people using the device, there is a lot of support out there if something goes wrong.
With many people using R4 cards in the DS Slot, a major problem that comes up is that the Nintendo DS stops reading the R4 card. This manages to happen on all models of the DS, and can be very frustrating. Below are a few of the reasons why this may be happening, as well as what you can do to fix the problem on your own. If you are still covered under warranty, then best send it in prior to trying to fix it, as trying to fix it may void the warranty.
Fingerprint on Card
A major reason why R4 cards do not work is that there is a fingerprint on the sensitive part of the cart responsible for relaying data from the cart to the machine. Though the particles may not seem like much, they can cause all sorts of havoc, and normally cause the DS to not be able to read the R4. Take the card out of the DS, and carefully wipe the card with tissue paper until all smudges are removed. It should go without saying that you should not use water.
Debris in Slot
Similar to a fingerprint, debris in the slot will stop the R4 card from coming into complete contact with the port. In this case, do what countless generations of Nintendo owners have done, and blow into the slot to remove any debris you can find. More often then not, this debris will float away.
A serious problem is if the connecter is destroyed. This means that something may be bent out of place, causing no data to be sent through. Most often caused by someone jamming the R4 card to hard into the slot, it may require taking apart the DS to fix the problem.
The bane of all electronics, water damage can cause the slot to stop working with everything.
The final thing to consider is a system failure, where the software got overwritten in some way and the DS is no longer able to connect. In this case, it may be time to get a new DS.