Custom Theme Disappeared

I’m trying to troubleshoot an issue with my WordPress Site (ver: 3.5.1) and one of the steps was to revert to the Twenty Twelve theme. The site also has a custom theme, however that theme does not show up in the administrative area under Appearance > Themes. I clicked on the Customize button under the Twenty Twelve theme, then clicked the close button without making any changes, now my site has reverted to the TwentyTwelve theme, which shows a blank page for my website. I can’t figure out how to go back to the custom theme that has been created for this website.

[Please continue – http://ww.wp.xz.cn/support/topic/pages-not-updating-5?replies=7 ]