Try to download http://www.ndsill.net/DSILL.rar and run the *.nds at a DSlite. If it doesn't work, you can buy a better card.

 

If you're on a Prince Caspian firmware, don't flash your firmware. The official firmware on the site is GUARANTEED to brick the cart. Devs were stupid enough to put a bricker up for download, the gall of them. Check the firmware, if it's dated 4/23/2012, it's a bricker. The one you want is the last good firmware they upped, which uses the Prince Caspian icon (that's why I call it that) dated 12/10/2011.

If however you're not on a Prince Caspian firmware (say you're on Finding Nemo or that japanese blue wolf icon), upgrade to the Prince Caspian firmware. Granted, it won't work on DSi 1.44 nor latest 3DS firmwares, but at least it's not bricked. Also, if you managed to brick your cart, unbrick it using that same firmware.

@raystriker: here's a little help for you too.
Get it here. I personally uploaded it, because it is currently unavailable for download anywhere. You'll need a working flashcart to unbrick a bricked flashcart. Just run the firmware updater from the working flashcart (get a device it works on-- DSphat, DSlite, even DSi/XL as long as it works on it and isn't blocked). When the updater runs and prompts to press A, DON'T. swap the carts (remove the flashcart and insert the bricked one) before pressing A. see to it the process finishes (sometimes it doesn't). if it reaches 100%, congratulations, you just unbricked the cart. now you can play it as usual on your DSlite, but it won't work on DSi 1.44 (yet).