Hey there, Mansoor Manuwar.
Well, unfortunately, more often than not when a flash drive or a memory card becomes write protected all by itself, there's a great chance that it might have failed. However, there are a few things you could try, hopefully one of the options helps you with your issue: http://www.wikihow.com/Disable-Write-Protection.
Hope that helps. Please let me know how it goes.
Boogieman_WD