Hacking DSTT does not load when turning the DS on?

[Random_user]

1.Nintendo's start screen(the one with the health warning I think) comes up.
2.DSTT starts loading but has a ''loading circle''(quite like the one you see when you watch Youtube vids) but stays like that forever. Screens are blank.
Edit: The loading circle is small and is in the bottom right corner. Is blue.
The SD card used that caused this loading problem had worked before. When taking out that SD card and putting in another one, it loaded perfectly. What's causing this problem and how can I solve it?

 

[Bri]

The usual suspects:

1. Your ROMs are all on the root of your microSD card. Solution: Put them in a "games" folder.
2. You don't have enough free space on your microSD card. Solution: Delete a few games.
3. Your microSD card has become corrupt. Solution: back it up and then reformat it.

-Bri

 

[Random_user]

Thanks, I tried no.3 and it worked.