Hey sorry for the delay. I am only on here once every other day or so.
On our server, we have the app.manifest and offline.appcache files located in a non-standard location, so when Construct was looking for them in the 'usual' place (which is in the web application root directory), it was unable to find them and simply displayed a black screen. I had to edit the raw html to adjust the symbolic link (the manifest="offline.appcache" on line 2 and href="app.manifest" on line 7) to point to the actual location of those files, which for us is manifest="/webres/offline.appcache" and href="/webres/app.manifest".
If you use Google Chrome with the Developer Tools running on the Network tab, it will show you if your offline.appcache and app.manifest files are loading properly. If they show up in red in the network tab, then your manifest files are not in the proper location and your game will just load a black screen.