Why is my ds game not working? PLEASE HELP!!

I bought Final Fantasy 4 used from Amazon.com and put it in my ds. All it does is go to a white screen when you start it........it'll work if you tap on the game while its in the system but then it just goes to the white screen again! I know there's nothing wrong with my ds because every other game i have works! Is there anyway to fix this? Thanks in advance!

Here's what I did to make mine work once. I took a thick-ish cloth and a toothpick and just rubbed back and forth a little bit on each reader, it's not as hard and doesn't take as long as it sounds :)