If your entire webpage is blank, reading this FAQ may help you. However, if you are seeing part of the interface, but the main window of the Dashboard is empty, please read this FAQ on blank tabs on the Dashboard. If you are not sure which issue you are experiencing, try both the fix in this page and the one in the other.
A completely blank page on the Dashboard may be due to different causes, but it may represent a temporary crash. If that is the case, you should be able to see the Dashboard once again simply by refreshing (reloading) the page. If this does not work and you keep seeing only an empty page, please use the bug report page or the "Found a problem?" button on the Dashboard page, if you can see it.
When reporting the bug, please specify that you have already tried what suggested here and attach a screenshot.