Please run the Command Prompt by typing CMD in the Start Menu search box. Open it as an Administrator and type the following command:
Select disk n (n must be number of the drive)
Check if the write protection is enabled. If it is, type:
Attributes disk clear readonly
Check if the pendrive is now working properly. Do you have important data on the drive? If you do not have, I would advise you to format it.
Check the link below for additional suggestions:
Hope this helps