Are there big red "X's" somewhere in your timeline?

No, no X's of any kind in the timeline.

If so, I think you accidentally deleted some clips and/or movie files. You can do a couple things here.

But when one edit the movie / clips [and move the bar where you want to cut the clip] does not that delete those clips?

1. Start fresh and edit all those clips over again.

True, it is an alternative. But if I do that, do I have to edit clip per clip? As I did this time, I brought all of the clips down to the timeline, and did then start to cut and edit. Could that have been the problem?

Am I supposed to edit one clip -> Save it -> Edit a new clip and so on...And then when I am done, bring all of those clips together at the timeline?

2. Find those movie files...garbage or different folder and restore them.

So if I manage to find them, I just have to go about it the same way as when restoring other files that have ended up in the garbage? Or do I also have to bring them back into WMM and find the "old" and previous location there again?

3. Copy and past all the clips into a new movie file.

I tried this, of sort. "Edit" --> "Copy All" --> Open a new project --> "Paste". I did encounter the same problem still though. :/ Or do I have to copy & paste clip by clip?

I used to make this mistake sometimes. Do not delete ANYTHING until you have saved your movie file.

Hmm...All these questions makes me wonder if I really should be making movies, haha. But still, how do I avoid not deleting anything while cutting and editting? Or do you mean that I should bring the clips down in the timeline; Save; then start to cut and edit? I wonder if I did not make the mistake of bringing the clips down to the timeline and started to editit the various clip without saving first.

Well, perhaps it is just as good to start over again since the "completed movie" I have now is 19 minutes long, which would have forced me to make two parts.