I think Eddy just quoted the wrong line. I tried clean installations of both Avast! and Windows. It turns out however, that the windows install wasn’t as clean as i thought. I have resolved the problem and my PC is just fine now ^^. For those who are interested I’ll explain the problem and the solution below.

First off, when installing Windows I used the built in tool (on the DVD) to format the HDD. This tool wasn’t working properly and I realised this when I saw that my HDD only had 1TB (out of 2TB) available after the installation (of windows) was complete. To properly format my HDD I found a guide on how to do it from cmd:
http://www.windowsnetworking.com/kbase/WindowsTips/Windows7/AdminTips/Miscellaneous/HowtowipeaharddriveusingDiskpartandFormat.html

With a clean disk i tried, once more, to install Win10. This time however I got an error message saying “On efi systems windows can only be installed to GPT disks”, which quickly brought me back to google. I found out that the problem was in my dvd drive. My “fiddling around” in Ubuntu had apparently changed the default “driver” (or whatever it’s called) for the DVD in BIOS. So i went into BIOS and checked out the driver for the DVD and I could swap it for another one that wasn’t marked “UEFI”.

The new DVD driver was able to install Windows properly and a clean wipe (using cmd, not the shitty tool on the Win10 Live Disk) was the thing that led me to it, as I didn’t have any errors when installing windows before the “real” wipe.

Most concering is that a Live disk is no longer able to perform a wipe properly using the graphic layout. I remember that it was possible to to both quick wipe and a full wipe with a WinXP disk without any difficulty.