A re-install will most likely yield no differences as all the setting files, that Cubase created upon your actions, won’t be deleted.
The thing is: You have Cubase Elements and probably expect it to be nice for getting into a DAW. However, Elements runs on the same principles then Cubase Pro does, especially in terms of the audio system.
The Cubase audio system is shielded so well against the Windows audio system that nothing that you do on the Windows side of things will have an effect on the Cubase system (except for installing ASIO drivers). There are good reasons for that but it makes Cubase cumbersome to work with when using consumer audio hardware like the Realtek audio chip.
E.g. the Realtek chip’s driver is not capable of playing back sound from Cubase AND Windows at the same time. It is either one or the other. That is also the reason why you lose sound in Cubase. Something in Windows is occupying the Realtek device.
The headphone issue is a completely seperate thing that has more likely to do with the Realtek settings.
Have a look at this: