This works if your mp3 player or usb flash device works fine with with other computers. 

Registry
Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. If uncomfortable with using Registry Editor, see if you can find someone who is comfortable and that you can Trust. Use Registry Editor at your own risk.

For Windows XP Only
1) Click Start->Run. 

2)Type regedit and hit enter. 

4)Click on the plus sign next to HKEY_LOCAL_MACHINE 

5)Click on the plus sign next to SYSTEM 

6)Click on the plus sign next to CurrentControlSet 

7)Click on the plus sign next to Control 

8)Click on the plus sign next to StorageDevicePolicies 

9)Write click on WriteProtect and click modify. 

10)If the value data is 1 change it 0 and click ok. 

11)Repeat steps 7 to 10 for ControlSet001 and ControlSet002 . 

12)Close Registry editor and restart the computer. 

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If you don't find it in the registry, the best way is to create it yourself. Below is the procedure.

Start the Registry Editor 

Go to the HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control key 

If there is no key called StorageDevicePolicies, create it
.
You do this by right-clicking the HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control key, and selecting New > Key from the menu. 

Select the StorageDevicePolicies key

From the menu select Edit > New > DWORD Value

Name the new value WriteProtect 

Right-click the WriteProtect value and choose Modify 

In the Value Data: box enter 1 

Exit the registry editor, and restart your computer 

"To reverse, just delete the new WriteProtect value (or set the value to 0) and restart the computer."