I think I need some help, tonight I made an extremely painful experience:
I've been using WP 3.3.1 with minimalism by Christian Genaehr on my website for almost a year now. Initially I modified the theme's style.css file (only header image, column sizes, spaces), which was almost okay, but had certain bugs that came from my severe ignorance with html and css. Well, it worked more or less.
Later I found out there was a "smart" way for doing this, so I tried to make a child-theme for minimalism and sort out the bugs. I was following the step by step instructions provided at http://codex.wordpress.org/Child_Themes
First, I renamed the already installed theme folder to minimalism-child, then I copied the unaltered original folder into the same wp-themes directory.
I modified the /* information header of the style.css file in the child folder according to the guide. Since this was the original theme's modified file already, I left "The part after the closing */ of the header" wich is supposed to work "as a regular stylesheet file" unaltered assuming it would override the parent file's code. Now my parent file was the unaltered original, and the child file was the original modified by me with a new child-header.
I did not deactivate the theme during this process.
First, the child theme did not appear on my dashboard, only after activating a different theme. Then I activated or at least was trying to activate my new child theme but I ended up with my dashboard AND website going absolutely blank.
Finally I removed the unaltered theme folder from the wp-themes directory, I renamed the minimalism-child directory to plain minimalism and restored the code in the style.css file to the initial state (that is, with my initial modifications).
My site and my dashboard returned to life, but the appearence of the blog lost the modifications I made to it. The content was there, the theme was there, only my column widths and header image went lost - while the css code is still containing the according information (I made a backup copy of it).
I'm pretty sure I made a mistake by not deactivating the theme while manipulating it. But I think there was something else too. This act of replacing theme folders somehow seemed to affect the functionality of the whole WordPress installation. Do you think it is possible to return to the initial state without asking my service provider to restore the database or whatever? What should I do differently next time I try?
I didn't want to display my messed up page publicly, so I redirected it to a simple text page, that's the reason for not providing a link here.
I would appreciate your help a lot.
Learning by doing is fun, but this time it was too much fun already.