If you want to create something like
Hirens BootCD[
^] then to be honest a .NET framework language is a bad place to start. They all requires the .NET framework running in order to work at all - and that requires the whole of Windows to be running first.
A bootable diagnostic CD should not need the "normal" OS or any components of it to run - as it should be diagnosing faults with that OS or the components it loads.
You really want to be looking at native code - which means C++ most likely.