SanDisk Cruzer Blade 16GB write protected error

do you know what’s causing this??  i had this problem wind a cruzer edge 16GB that I returned to the shop, then they gave me a cruzer blade 16GB, 3 days later is write protected as well!! iam trying everything and nothing seems too work! the only thing that changed in my computer last week was some win7 optional updates that I installed… I have no virus, spyware or malware!! scanned dozen of times. Iam going to return the second flash drive but iam afraid it happens again…

a little help here…