Have you repaired permissions?
I am no sure what that means. But it will allow me to save to the desktop, but not to my harddrive or external drive
it is a brand new laptop, so is there a default setting I need to change,or something to allow it to save indesign files to the harddrive?
More info would be helpful.
OS version? ID version?
Sounds like a permissions problem.
If on a Mac, open Disk Utility and repair permissions. Set read and write permissions on your external drive.