Thanks for using Apple Support Communities. Since it sounds like you've isolated the dark display after waking down to being user-specific, I recommend the appropriate section of this article:
If the issue occurs in only one user account
If you have isolated an issue to a single user account, then you should focus your troubleshooting on that user and specific application(s) that are problematic when logged in as that user. Mac OS X: How to troubleshoot a software issue provides some assistance with this, although if you are just seeing the issue in one account, you most likely do not need to reinstall any applications.
If you are seeing issues with an application unexpectedly quitting in just one account, see this help article for additional assistance in OS X Lion. See this help article for additional assistance in OS X Mountain Lion.
Other, application-specific issues isolated to a single user account can often be caused by a problematic preference list or setting. Check the application's documentation or support website for instructions on troubleshooting specific preference or setting files. For example, iLife preference troubleshooting is documented in iLife: Troubleshooting Basics. If you are looking for assistance troubleshooting a specific alert message or issue, you should try searching the Apple Support website.
If you need further assistance with troubleshooting an issue isolated to a specific user account, you may wish tocontact Apple Support. If you work with AppleCare to troubleshoot the issue, be sure to let them know about any troubleshooting steps you have already performed and the results, and the text of any alert messages you have received. You may wish to take a screenshot of any messages (see this article for OS X Lion or this article for OS X Mountain Lion), so that you can use them for reference and provide them if needed.