My guess is, you recently ran Windows Update and you got a brand new browser version. Internet Explorer11 (or 10) is no longer compatible with Network54. You can, however, fix that problem.
They hide it fairly well, but if you go to your browser's "Tools" settings, you can turn on "Compatibility View" for Network54. This will turn back to IE9, which was the last fully functional version of the browser. In IE10, it's right in the area that shows the URL, in IE11, it's no longer there.
This will not change your browser for any other website. If yo find other sites that no longer work, you can try the same for each of them. It doesn't always solve the problem, but it's still worth a shot.