I found a solution:
I created a bootable USB and burned Windows on it.
During startup I spammed F8. Then came to a menu in which I could choose whether to boot from the hard drive or the USB. It even had the specific USB name.
I chose to boot from the USB and it worked.
Conclusion: It was apparantly my DVD drive that wasn't working properly.
Sidenote: Installing Windows from a USB is a lot faster than CD.