As it turned out, my walls were deleted as they infringed copyrights.
I did not know that making wallpapers based on existing anime or media was forbidden because I've seen SO many of those scattered all over the web that it amazes me this is not allowed here.
Another reason why I can't fully understand this is that at least two of the works I used are outdated and the companies making them don't even exist anymore, thus they cannot make money off it. Other forms of art use resources from those works in game mods, fan music, wallpapers or other visual art, without anybody complaining. I guess there is an accepted difference between stealing existing anime art, and using this art in fan works to honor the actual source. However, if this difference is not made on deviantART, I guess I won't be able to submit much of my work as I base most of my art on existing sources.

By the way, the Nickelback CD cover is copyrighted too, so I wonder why that wasn't deleted.