I don't know if this has anything to do with it or not, but I would suggest getting a lot of the book images and such out of your sidebar and into a page. What you might try doing is go to appearance > widgets and temporarily move them out and into the "inactive" widgets area at the bottom of the page and see if that fixes the issue.
It also might not be the number of widgets, but perhaps some code in one of the widgets that is causing the issue.
The W3C validator is reporting 58 errors on your page, but many of them are trival. There are two though that can cause issues and that is a missing end tag for an image tag, and a missing div tag. Both of those can cause sites to blow up.