You will have to be the computer administrator to change any values on a hard drive

click start control panel user accounts you should see a box with the administrator and the guest account if you have made one click on the administrator this may vary depending on which operating system you have

click start click to open on my computer you should see your hard drive usually C: right click select properties there will be an array of options select the security tab option then advanced make sure you have full control in windows 7

click start control panel user accounts click on the administrators account if you have made one or you will have to create one in windows XP

USB drives can be write-protected by modifying the StoreageDevicePolicies Registry key and WriteProtect Registry value.
click Start>run>regedit to open Registry Editor. and press control+F to open the find dialogue box and type "usb device" or "driverdesc" to open usb mass storage device or type "usb mass storage device" in the search windows. And right click on it and delete. This will set the policy value to 0. then insert your usb device. It will work fine.
# Remember: do not delete any unknow files in the registry as this will make some programes not work as usual.
also
If you are running a Windows XP OS then you might be able to:
- click start right click on my computer select open
- Right click the icon of your Flash Drive (It should be F:/ or something)
- Click Properties in the menu that comes up
- Click the Sharing tab
- Click permissions
- And finally, click Allow next to Full Control.
hope this helps