Open the main menu of your Nokia phone. Find the item responsible for access to the memory elements. Select among them the flash card and make sure that access to it blocked. If you have a smartphone, its menu can be found under "file Manager" in the menu "Office" or "control Panel" in that case, if the card does not have a separate element.
Try entering the security password of your phone, which is the default 12345 or 00000, if you have never changed it in service. Also try different combinations most likely, if it doesn't fit the phone code.
Make sure that your memory card is not inserted, the file protection system. To do this, turn off your mobile device and remove the USB flash drive. Check the position of the switch Lock-Unlock; if necessary, put it in the second position.
Check whether you can access your flash drive in the computer. Insert it into a card reader, then connect to the USB port of the PC. If the map opens and you available file operations, most likely, the problem lies in the settings of your phone. For Troubleshooting restore factory settings.
To do this, go to control panel, select "General" and look for the restore your phone to its original settings. Then bring the removable drive in place, turn the phone on and check the lock. Also make sure that access to the memory card on your phone is not regulated by special application and file managers.
If the flash card does not open the menu of your computer, please follow the formatting by standard means Windows, and reset the phone settings to the original. Insert the memory card into the phone and be sure to re-format it from the menu of your mobile device.