try this ..
download and unzip this to a directory on your pc
http://www.dsgba.com/down/nand_stable_26.zip
you should end up with 2 files called copy xmenu.dat and autorun1.nds
1. Grab your NDS and plug in storage card & Fire Link cart
2. Connect USB cable between PC and Fire Link cart, power on NDS
3. Select USB Mode, and you'll see a new drive letter mount for the storage card
4. Browse to root dir of new drive letter, then copy over the two files you unzipped in the first step ( xmenu.dat and autorun1.nds )
5. turn NDS off and on. Select Menu instead of USB Mode and a command line BIOS update will run. Hit A to perform update. When done, restart NDS.
6. After reboot, select USB Mode and delete autorun.nds. Restart NDS.
see if that works
Dan.