Windows 10 Minecraft can't sign in to my Microsoft Account

Sign in the Microsoft Store with the old account. Then, install "Minecraft for Windows 10", it should be free. After that, sign out your old account from the Microsoft Store. Open up "Minecraft for Windows 10", then sign in with your new account. You will
get updates for free if you do the following. I hope this helps.

Hi AquaGarnet67,

sorry to hear. Please check if your System is uptodate (via Windows update and also the Windows Store APP). Check if all the 4 XBOX Services are running (via taskmanager / services) if this is all fine try to repair/update "Xbox Identity Provider".

Hope this helps and please keep us informed

When you redeemed your Java Minecraft on Mojang, you have gotten a 5x5 code to redeem Minecraft on the Windows 10 store.

This redemption is a separate service of your Mojang account, and it's possible to use a Microsoft Account email that is different from your Mojang account email.

Mojang (which gives you Java Minecraft) is separate from the Microsoft Windows Store App, which uses a Microsoft Account email when you redeemed that 5x5 code.

After redemption of that code, the Windows 10 Minecraft is tied to the Microsoft Account email you used on your Windows 10 PC. From then on, you don't really need the Mojang account anymore, if you only want to play on Windows 10. You will then get the game
from the Windows 10 store only, with the E-Mail account you used on the Windows 10 store during code redemption.

So make sure you are signed in with the Microsoft Account email (which might not necessarily be the Mojang account email) when you use the Windows 10 Store app to re-download your Windows 10 Minecraft again.

Let me explain. Minecraft was bought in the Microsoft Store using a different account. Then that account signed out and my account signed in. I am 100% certain that I bought the full version of Minecraft Windows 10.

(EDIT) Also, it's the DEVELOPMENT beta, like the Xbox Insider Hub beta.

Players who already have the previous PC or Mac edition of Minecraft (running on Java) can
download Minecraft: Windows 10 Edition for free.

Note You'll need to get a code from Mojang, the game developer, by signing in to your Mojang account before attempting to redeem your code for Minecraft: Windows 10 Edition. Otherwise, you
may incur a charge. To get your code from Mojang:

1. Sign in with your Mojang account.
   
2. Under Minecraft: Windows 10 Edition, select the link to request a code. Microsoft Windows 10 will open.
   
   Note You'll need to sign in to or create a Microsoft account. If you sign in, use the Microsoft account you use to sign in to your Xbox account.
   
3. If you're running Windows 10, you'll be able to download the game right after redeeming your code. If you're running an earlier operating system, you'll need to come back to Microsoft Store once you're running Windows 10.
   

The code you receive from Mojang will be kept on your account, in case you’re unable to redeem it straight away, or in case you have problems trying to redeem it in Microsoft Store.

For more info:
https://support.xbox.com/en-US/games/game-titles/minecraft-windows-10-edition-faq