Entire timeline vanished in Final Cut Pro!

If your drive is full, start by deleting generated files. Select the library in the browser sidebar and do File->Delete Generated Library Files. Check all the boxes, including All render files.

Now select the long clip and do Clip->Open Clip.

Do the contents show what you expected to be in the project?

If so, select All, Copy.

Then create a new project with the desired frame size and rate, and Paste.

Are you sure you edited in a project.

It is quite common for beginners to edit inside a clip container instead of a project.

Look in the browser and see if there is a clip whose duration is about what you expected your project to be.

Double click the project in the browser. What happens?

Shift-Cmd-4 and drag a region you want to show. It saves to the desktop. In the reply box, at the bottom, there’s a button to insert an image. Click it and find the screenshot on the desktop.

It looks like there’s only a gap clip on the primary storyline.

Open the 45 minute clip. Post a screenshot of that.

You seem to have a Gap Clip (that grey bar) sitting in the primary storyline of the project.

What else is there?

You may click anywhere on timeline and then press Shift-Z to zoom to fit, so you see all the contents of the project at once.

This is a compound clip. You have several of them.

I can only surmise that you somehow got into editing inside this compound and did not realize it.

You can:

a) select All, Copy, open the project, Paste.

OR:

b) drag this very compound clip to the project timeline, and then "break it apart" (select in the timeline, and do Clip->Break Apart Clip Items).

That's a compound clip. You seem to have a number of them. First, select everything in that compound clip in the timeline Cmd-A and copy it Cmd-C.

Use Cmd-N to make a new project. Name it and set the specifications to match your media. When the project is open paste everything you copied Cmd-V.

can you post a screenshot of the project in the browser?

Luis’ question is a likely other possibility.

You said there was a clip that was about 45 minutes long. Can you find that clip and use Open Clip and post a screenshot of the timeline. The more we can see the better.