It's not blank. It's got some characters on it. They show up on your main page too, right next to your warehouse image.
When a visitor clicks on that the category link, those characters are the first thing to be sent to the visitor's browser, and they arrive too early. I'm betting that they are followed by an warning and then a fatal error that the "headers have already been sent" which also gives the file and line number from which they were sent. Trouble is warnings and errors have most likely been suppressed by your web host, so these very helpful clues are not available.
Options: you could ask your web host to turn warnings and errors on, but they'll probably refuse - they might however, depending upon the type of server you are on, be able to suggest how you might be able to turn them on locally, and find out where the problem is.
You can download all the files that make up your site and compare them to a clean set of files to try to find where the problem is.
Or you could just upload a fresh set of files, though you would need to move your template away from the classic folder to avoid over-writing it (there's info on using over-rides in the FAQ).