i can't drag and drop to my seagate external drive

Hi there, seems that your disk is read only.

Restart your Mac, in most cases - if you were able to read and write on your External HD before - restarting will fix it.

You can find out if the external HD is read only Get information about a disk on Mac - Apple Support or by right clicking (or the equivalent of right click on a trackpad etc) on the disk and from the menu select "Get info", if your user name is not listed at the bottom - Sharing and permission you might have to add it.

Try to Change permissions for files, folders or disks on Mac - Apple Support.

Good luck

A

Restart in Safe Mode per the directions in Use Safe Mode to isolate issues with your Mac and then retest the computer.