I assume that it was a fully functional router prior to this?
If so, when did this problem occur?
If the flash card is corrupt, you can either get it replaced via RMA if you have a support contract, or try accessing the files with a hard drive. The flash cards are readable with in a laptop running Win95/98. You could check out the files, see if they are corrupt, and if they are, just delete them, format the card, then put fresh files to the card.