FCPX not importing video and not rendering or sharing anything previously imported.

You can send events from iMovie. You can also open the iMovie library bundle and copy or move the clips out of it You might try the QuickTime player to import.

what is the external drive? How is it connected and formatted?

Make sure FCP has Full Disk Acces in Privacy settings as well as external disk access.

In addition to what Tom said: whenever something is not right, delete the application's preferences.

To delete preferences, hold down command and option while starting FCP X and click Delete Preferences.

The application will start in a default state, and open an "Untitled" library. Reopen the library you were working on, set the preferences the way you like them, and try again.

Reinstalling is an option.

You can use the FREE FCS Remover which will get rid of most of the hidden FCP files.

https://www.digitalrebellion.com/fcsremover/

When you download FCP X make sure you copy it onto a separate hard drive so that should something become corrupted at a later date you don't have to wait for it to download again.

Probably the best way of removing problems is to completely erase your Mac and reinstall everything.

This puts your Mac back to its "as new" condition and gets rid of all the dross that accumulates over the years.

The whole process takes a few hours but you don't have to be present all the time as the computer can be left to do the work.

Needless to say, YOU MUST BACKUP EVERYTHING BEFORE YOU START.

I tend to do it every couple of years.

Here is something that I don't understand:

If you only have a DV clip in the timeline, with no effects or transitions, there would be nothing to render.

I cannot get anything to render in FCPX either automatically or manually. The project consists of one 13 minute DV clip with no effects or transitions of any kind.

Regarding the Etrecheck report, I do not see anything standing out. You probably don't need the LaCie software, drive manufacturer's software is not needed and often cause issues. You could try uninstalling it, but I doubt in this case it was the cause.

What version of FCP X? I don't think you mentioned that...

Glad that it is working now!

I don't think it is surprising that the drive itself is owned by system, with group wheel.

What I did find surprising was the solution itself, given that often one does just the opposite... but it is working, as that is the main thing.

Please run Etrecheck and post its full report here.

There may be something else that is interfering.

Is the problem only with tape based media, or file based media also?