Blank page when I try to preview my entry

Hello
Yesterday I receive this e-mail:

Howdy! Your site has been updated automatically to WordPress 3.9.2.

I have four wordpress blogs and I received this e-mail for all of them but I’m only having problems in one.

When I’m writing an entry and I want to preview it, it opens a blank page (with blue background). I can’t preview my entries before I publish it. I test it in the rest of the blogs (one of them has the same layout) and it’s working fine.

I think it was a template problem and I change it, but nothing changes. I install wordpress 3.9.2 again but the problem it’s still there.

Any idea?
Thanks!