Does the drive have a little switch on it that makes it read only ? If it does flick the switch and reconnect it.
Its also possible that the computer is trying to assign a drive letter to the usb pen drive thats already reserved. If you are using Windows XP then right click "My Computer" left click "Manage" left click "Storage" and "disk management" you'll see a list of available drives and assuming you can see the drive in the list by right clicking you can change the drive letter.
Lastly if you are in a work environment its possible your IT people have set a system policy to prevent the use of usb devices. So it may be worth asking them.
Good luck
Teve
August 2007