If you scroll down the front page, you will see that the sidebar is indeed visible. It has just jumped down beneath the content.
I recognize this situation. Usually it comes down to an extra closing </div>
tag somewhere in a post’s content. This leads to incorrect nesting of the html and the layout gets screwed up.
Check your site in a validator and see for yourself. Here is a quick check. There are several errors of incorrect nesting and one error of missing ending quote. This is a good starting point to fix. The error is not in thematic but in your post’s content. The culprit is probably the missing closing quote.