I had a problem once with a SanDisk SD card, I didn't have the reciept or packaging either. I sent them an email on the tech page with the problems and they said they would replace it so I just mailed it into them and they sent me a new one.
Also one time I acidentally deleted the partition for my SanDisk Mini Cruizer while I was installing XP
I just repartitioned it and formatted it and it's working fine.