First try refreshing the page. If you are using multiple monitors, try dragging the browser window onto the other monitor.

If you still cannot see anything in the 3D editor window (not even the default grid), its likely that your computer doesn’t support the 3D graphics features the Plattar CMS requires. 

To check your computer try visiting this link: https://get.webgl.org/ if you see ‘Your browser supports WebGL’ and a spinning cube but still cannot see the editor, contact our support team. If you see a warning that your browser does not support WebGL, try another computer or browser.