1. Go to the client machine and
2. go to start button and type in to search box gpedit.msc
3. then your group policy window will open
4. left side of window – search Administrative Templates and double click on it
5. then click on System
6. next you will see Removable Storage Access just click on it
7. then you will see lots of group policy name
8. see the All Removable Storage Access: Deny All Access
9. double click on it and select the option Enable and click on OK button
10. you will success to block USB of client

Then from cmd run ==> gpupdate /force