Board Thread:Support Requests - Getting Started/@comment-26156026-20150417221257/@comment-452-20150417235859

That should not have been possible, unless that person was an admin. Did you recently appoint new admins? Ask them to undo whatever it did.

As per your main page, if you've edited in it the past, check your contributions: Special:Contributions/NChad,  Special:DeletedContributions/NChad.

It is possible the other admin also changed, MediaWiki:Mainpage which would explain why you can't find it.