The description indicates that it is likely to be a virus or some malicious software issue.
First off let's check if the files/folders on the drive are recoverable. If the files can be recovered you can run an antivirus scan on the drive and can retrieve your files.
Follow the steps below:
1. Boot the computer to Windows XP desktop (your profile mentions your computer has Windows XP).
2. Click start.
3. Click Run.
4. Type cmd and click Ok.
5. Once the cmd prompt with black background appears type the following and hit Enter:
attrib -h -r -s /s /d f:\*.*
(Assuming f: is the drive letter for your USB flash drive in my computer.)
6. If the cmd prompt displays the list of files/folders, you can still recover them.
7. Run full scan on the USB flash drive using your antivirus software.
8. If you are using Windows XP 32-bit then you can get a free antivirus software from Microsoft.( http://windows.microsoft.com/en-US/windows/products/security-essentials/download
9. Once the scan is complete or during the scan do select to remove the malicious content from your computer.
10. Hopefully, you will be able to recover your files on the USB flash drive. This worked for me.
Do reply with results.
Thanks & Regards