Recently I've had an issue regarding the load-styles.php stylesheets in the wordpress admin. The problem presents itself by not loading some admin stylesheets; for example: the stylesheet '../wp-admin/load-styles.php?c=1&dir=ltr&load=admin-bar,wp-admin&ver=3.4.1' presents itself as a blank page in Firebug's css editor and shows 0 rules in Firefox's Style Editor.
Loading the stylesheet directly in the browser presents either a gzlib error or a 'page not found' page. Curiously if you change the 'c=1' to 'c=0' the stylesheet loads correctly. This suggests to me that compression is failing in the load-styles.php script. It also suggests, since the stylesheet issue has only presented itself in the last week, that there is an error occurring with gzlib on my hosting server, and that the issue is not with wordpress.
The easiest way to resolve this without editing the core wordpress files is to change the value of 'can_compress_scripts' to 0 in the options table of the wordpress database (typically wp_options). I'm not sure yet of any possible conflicts that can occur by modifying this value. To be extra cautious, I'd recommend re-installing wordpress and re-creating the wordpress database on your hosting server first.