Windows 10 installer not starting, instead tries to load a non-working installation

I installed Windows 10 on a colleague's PC, but after she accidentally connected the monitor to the motherboard instead of the graphics card, it started missing winload.exe (interrupted some update maybe?). So I bought the USB stick with the Windows installer to work, but now it instead just tries to load the installation instead of giving me the option for fix or anything. It doesn't even let me reinstall Windows, let alone to select an option for fix (I got the "fixing windows" though after a few bluescreens).