Well…I have this exact problem…
I have a Sandisk Extreme Pro 16GB SDHC myself…Worked great untill yesterday, when it apparently figured it would be a good idea to go die or something… This severely pisses me off, I’m unable to format it, I’m unable to write to it, I’m unable to delete anything… And here I go buying SanDisk due to needing something that will last 
I’m calling the shop I bought it from… The card is just over 2 months old, sure hope these cards are supposed to “live” longer than this.
