If it's under warranty send it back. It sounds like through a combination of installing a theme (stupid mistake 1), semi-bricking (stupid mistake 2), and installing the 'wrong things' (stupid mistake 3) you have totally bricked your Wii.
You may be able to launch recovery menu using the GC controller trick but the likelihood of recovering with that level of corruption is very unlikely and would cost you a fair amount.
Never install a theme on a Wii that does not have bootmii/boot2, Preloader is worthless with System Menu corruption.
Provided you have a black screen on start up then Nintendo will have a hard time discovering the mess you made and probably send you a refurb. Say you got black screened when you did a NSMB disc update or something, don't use the word brick.