This problem might be caused by malware or a virus. To fix this, you firstly need to open Command Prompt using Administrator rights. You can find it under Start > All Programs > Accessibility > Command Prompt. To open it as Administrator, you just need to right click on it, and select Run as administrator. In the CMD, type
attrib *.* X: -r -s -h /s /d where X: represents the letter for your pendrive drive and hit Enter. After you did this, I suggest you download and install Malwarebytes, update it and scan your pendrive. This should fix your problem and you should be able to use your pendrive again.