Bought a new Sandisk 8GB microSDHC card (Product

Bought a new Sandisk 8GB microSDHC card (Product Description : Micro SD/8GB SDSDQ-8192-P36M) for my Nokia E51. It worked fine for two months, in this had many times used in PC with my card reader for transfering files. Suddenly one day my mobile got hanged after that the microSDHC card became unreadable. I tried to check it in PC, first it showed the files and folders but neither of them was readable so i tried to format it but formatting was unable to complete. Its almost four months over now i tried it in many PC's and mobiles its unreadable now when inserted just shows a removable drive neither you can read it or format the card.