I already tried everything.

Going to default programs. Associate a file type, etc.

But it doesn't work. All of it.

I want VLC as my default player. Whenever I choose a file it asks me to open it with, I always check the "use this as default thing" and I will browse for VLC app. And it won't start. So I have to manually do it.

Plus, my Windows Skype won't load. It will just stay at the task bar whenever I will click it, it'll open then close immediately.

And whenever I try to download an app from the Store, it won't finish downloading. An error says: 0x80070002

HELP. I don't know what else to do.

*Sorry for my bad English...

refresh you Windows and check the results ;

http://windows.microsoft.com/en-IN/windows-8/restore-refresh-reset-pc

Actually you can achieve what you want easier, just right click the file that you want it the be played using VLC, and click "Properties" and you'll find "Opens With:" and Default Program, Click "Change" and choose VLC

I know it's not an answer but a Temporary Solution.  

refresh you Windows and check the results ;

http://windows.microsoft.com/en-IN/windows-8/restore-refresh-re

Hi,

It appears that there are 3 issues on your computer:

1. Cannot change the VLC as default player:

You can try the solution  here, consider that you have no permission of the related registry keys:

Fix: Unable to Change Default Program Extension on Windows 7 | 8
http://www.thewindowsclub.com/fix-unable-change-default-program-extension-windows-7

2. Cannot open Skype and it always crash.

For this issue, you can try the app troubleshooter to see if there is any exact error about this program:

Troubleshoot and Fix Apps problems with Windows 8 Apps Troubleshooter
http://www.thewindowsclub.com/windows-8-apps-troubleshooter

Also, you will see the related error under event log, you can also post back the event log for our research:

3. Error code 80070002 appeared when you try to download app from Windows store:

Try to clear store catch:

a. Press "Windows key + R".
b. Type wsreset.exe and click OK.

Run the following in a Command Window (CMD) to re-register the Store App:
powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.XML

If you get any antivirus program, please disable it and check the store