04-10-2014, 06:22 AM
Steve, are you able to copy/move files within your main HD? From a desktop to a folder?
What about copying files from a Documents folder (your desktop is not really an intended storage place for your files) to say, Downloads folder, or vice versa?
If any of these are giving you errors, go to Disk Utility, select your main HD and click Verify Disk Permissions, wait for it to finish, and if it lists any errors, click on Repair Disk Permissions.
You've mentioned USB sticks and external HDs - are these all newly acquired? If not, were you able to use them before? Can you see files on, and can you copy a file, from external USB storage to your main HD?
If there's nothing stored on a particular USB drive, try to reformat it, after verifying it is indeed formatted correctly, as lifeisabeach
Also, rather than drag-and-drop, can you try CMD-C and CMD-V ? Shouldn't make a difference, if everything is configured correctly, but if it does, it'll be a clue...