Access may be denied due to several reasons.
Some flashs have locks on them to prevent erasing and writing. Some operating systems may not permit external devices. Also bios configuration should include USB ports. To identify your problem, please give all details.
1. Operating system
2. Can you see the flash disk in My Computer?
3. If you can see, can you click on it?
4. Can you see the directories in the flash disk?
If you can do all these but cannot access the directories, just copy them to your computer and format the flash drive.