[HELP!!] Files all missing while I update the version from Unity 2018.3.12f1 to Unity 2019.1.4f1

I update my unity from 2018.3.12 to 2019 1.4,and open my 2D project with new unity.

It says that my project need to be upgrade.

But when the progress finished,it opened a 3D project and my assets and my scenes were all cleared.

Even if I open the explorer, the files in the assets folder were all missing but an image.

The image was the last one I imported in before I update.

The size of the project folder now is 52mb.

I try to reopen my project with 2018.3.12 version,

But it says that:

1. An error occurred while resolving packages:
2. Project has invalid dependencies:
3. com.unity.package-manager-ui: Package [com.unity.package-manager-ui@2.1.2] cannot be found
4. Package com.unity.analytics@3.3.2 has invalid dependencies:
5. com.unity.ugui: Package [com.unity.ugui@1.0.0] cannot be found
6. Package com.unity.textmeshpro@2.0.0 has invalid dependencies:
7. com.unity.ugui: Package [com.unity.ugui@1.0.0] cannot be found
8. A re-import of the project may be required to fix the issue or a manual modification of /[my project path]/Packages/manifest.json file.
9. Click on Retry to relaunch Unity and reopen your project.
10. Click on Continue to launch Unity. Some or all packages may not be imported which may cause compilation errors

I retried several times but all the same error.

And I click on continue, it opened a 3D default project with nothing just like I opened in 2019 version.

Can someone help me? I'm really worry about my project.

 

This doesn't sound good. I really hope, you by mistake have opened some other project. I've never seen Unity deleting all the files in the assets folder.

That's because these packages have been updated to the newer versions, compatible with 2019 and no longer compatible with 2018 or not even existed in 2018. To fix these exact errors you need to change the version numbers manually in Packages/manifest.json file. Open manifest.json from any other 2018 project and use it as a reference.