"Unable to start HTTP server. You may need to restart Construct2 with admin privilages, or use disk mode."
It seems the local server provided for testing has some failure. You can always go in the project properties and set "Preview mode" to "Disk" and check if it does work. Some functions will be missing (such as audio which will work only in http).
Do you use some sort of local server to work on websites or something ?
Also, is it specific to a project in peculiar, or does preview fail on any project you make/open ? (let's say you create a new project, leave it blank, try to preview it, does the error occur ?)
So I guess easyphp is making some kind of incompatibility with the local server ash uses for the previews.
I used to use easyphp, and dropped it in favor of WAMPserver (at some point easyphp couldn't even handle the installation of a Joomla). If the use of easyphp is not absolutely necessary for you, I'd suggest you to uninstall it and switch to another local server software.
That's really odd, normally a grey screen like that means an error occurred, and the error is listed under 'Console'. If there are no errors I'm not sure what to say! I've never seen that happen with no errors before.