I am desperately in need of advice.
OSX 14.4.3   iMac

I had a folder of photos sent to me from a friend and one item looked
strange. Small coloured icon. As I didn¹t know what it was I moved it out to
the desktop. Everything stopped!   The finder would not work. I had to turn
it off to restart as the Apple menu would not function.

I restarted and the finder will not work. It just keeps flashing. Nothing on
the top menu bar works.
My dock appears but the Hard Disk icon or any other folders normally on the
desktop appears.

I have rebooted from my external back-up disk (thank God for it) and trashed
the Finder preferences and desktop preferences. All to no avail. On
rebooting the finder continues to flash and the computer is unusable.

I am sending this from my external hard disk and everything works as normal
from this disk. It is a software problem.

Before launching into a complete re-install of the OS is there any other
course of action?
Would I be advised to buy Disk Warrior and try that?

This has never happened to this computer before.

Lloyd