I was in Join Avenue and I went shopping at Julie's Shop and bought her set of 12
carbos then the glitch happened after I bought them right after my money went down
my DS goes black and theres a loud BEEEEEEEEEEP!!! A blood curdling beep! Then the Power turned off! WHAT HAPPENED?!
Ok your Game cartridge is damaged. It is nothing to do with Join Avenue so you can't push that to one side. I have been researching this and I found that the ONLY way to make your DS beep like how you described is if you have removed the Game Cartridge whilst the power is on. Even if you think your game is of just wait a tiny bit longer then the Cartridge won't get damaged.
Your other game cartridges shouldn't be affected but in the long term your BW2 maybe affected.