Hi everybody. I haven't had any problem anymore for a few weeks. Unfortunately I don't exactly remember what I did, but it fixed it. I checked what I installed since my last post: I installed the latest Touchpad drivers (that was for a memory leak issue) and WiFi drivers. I suggest you try this as well, and please confirm if this was indeed the solution.
Have you still had complete success with this? Mine seems to be getting worse: for the past week or so, I come up with my display not detected EVERY time I turn the computer on, whether it's only been asleep for a few minutes or a whole weekend. I don't think I've changed anything recently, so this uptick in the failure rate has me a little worried.
I say "display not detected" because the touch input continues to work. With an external display connected, I looked at the Device Manager, and under "Monitors" it only showed the external display. I could still use my touchscreen to interact with the OS. I tried "scan for hardware changes" to see if the panel would register, but to no avail. Putting the computer back to sleep and waking it up again brought the screen up, and added "Generic PnP Monitor" to the Device Manager.
So far, this has only been an annoyance; I haven't lost any data or sessions from this wake-sleep-wake ritual. One comment is that I did have to install a graphics driver obtained from Intel directly a few weeks ago, rather than through Dell, because the most recent Dell-supplied driver was throwing errors relating to "Intel Display Driver stopped responding" on some wake attempts; in other web discussions, I found people mentioning how to force the XPS 12 to use a newer driver version in which that issue was resolved.
I can see this thread isn't getting a lot of activity, but I'll post this update in case someone else finds it useful down the road. I've found a connection between this behavior and however the system keeps track of opening and closing the lid. If the machine wakes up with no screen, I've been able to bring the screen back 100% of the time simply by closing and reopening the lid.
It's possible that my version of this problem only happens to people whose computers don't automatically sleep when the lid is closed, which is a non-default behavior. I'll quickly describe the steps I took to identify this solution, in case anyone is interested.
By default, my system was originally configured to go to sleep if I closed the lid. I always manually put it to sleep before closing it, so I wasn't aware of that default at first. But likewise, I prefer to open the lid and then wake the machine (in case I want to clean the screen, for example). However, I found it waking up immediately upon opening the lid. When I disabled the closing-the-lid-puts-computer-to-sleep setting, this behavior ceased, but that's presumably when no-screen-at-wake began. I didn't think to investigate this direction until a day when I didn't close the lid, because the computer stayed at my desk. I put it to sleep and woke it several times over the course of the day, and the screen turned on correctly every time. I've also confirmed that when I close the lid while the machine is awake and an external display is connected, the internal monitor disappears from the device manager, and reappears when I open the lid.
Didn't know what I was getting into until I started reading these Dell Forums. Just want to report that I have both these issues on recent new laptop.
XPS 12 9Q33 with i7 4510U CPU. Intel released that CPU recently in Q2 2014. This suggests this laptop model line is still suffering from wake from sleep blank screen & image retention issues that a lot of others have reported from over 1 year ago.
Wake from sleep issues - XPS 12 9Q23
Wake from sleep issues - XPS 12 9Q33 Haswell CPU
7/2013 Dell A02 BIOS acknowledging wake from sleep issue with possible fix, but even the newest A06 BIOS doesn't fix the issue to this day 8/2014.
Screen Image Retention - XPS 12 9Q23, 9Q33
http://en.community.dell.com/support-forums/laptop/f/3518/t/19497269.aspx (66+ pg of complaints)