This looks like one of three things : (1) Assuming that the display is lit with LED’s, it looks like one or a couple LED’s burned out. (2) It could be a locked or stuck pixel , to which I would use UDPixel to run the undead pixel dot at a space of 5x5 and move the flashing dot where the spot is for a few minutes. (3) Finally, it could be a dead pixel with no real solution, and you can either accept it, or look into replacing the monitor. All of this is given without any guarantee of fixing the issue, and is my personal opinion.
Peaty sure I got this figured out. First off, 3DS games have there contacts slightly higher then DS games. So, after I found that out from close inspections, I decided to press a little on the label side of the DS games that don’t work and every time they read. It would seem that the pins that make contact have been pressed slightly higher then they should be, so at some point I’ll open this bad boy up and gently raise them. The person I purchased this from had only one game (Pokemon Y) and left it in the system all the time, so I’m theorizing this caused the pins to be pressed higher then they should be over time. Cleaning the game contacts also helps, but that’s hit or miss. Pressing up on the game always works. Once the system sees the game, there is no issue until I remove it and place either it or another DS game in. Any other input will be appreciated.
You would need to either provide the exact model, what it won't play, and what is there are any error codes for someone to help you. Otherwise, you can contact Samsung about it and if it's in warranty, they should fix it. If not, they will either charge you or depending on the age of it might not repair it at all.