You can easily remove write protect problem from the 16 GB HP pen drive, you need to follow some steps
1) completely scan pen drive by using best antivirus application and fix virus
2) Run bellow mention command on DOS
? Write "DISKPART" cmmd and press enter
? Write "list disk" cmd and enter; now you will get the presented disk list.
Now check the drive from the list and note down beside number of this disk
? write "select disk 2" cmd and enter now you will get the message that disk 2 is now selected
? Run this cmd on Dos: "attribute disk clear readonly" and enter
Once entire task is accomplished then exit from the DOS Shell, now write protected problem is resolved.