laptop - Keyboard on new notebook works only until typing in the Windows account-password

I'm setting up my g/f's new Acer notebook (coming pre-installed with Windows 8.1) via TeamViewer. For some reasons the internal keyboard completely stopped working. It works until she types in the password for her Windows-account but then nothing but the Windows-key (to activate the tile-view) works.
The trackpad works without flaws.

I can use my own keyboard via teamviewer.
It looks like a hardware-problem but since the keyboard works until she's inside of Windows 8.1 this is just strange.

Does anyone have a slight clue what is going wrong?