Change and recheck Power Options to see what the Settings and Advanced Settings show for closing the lid. Change it to what you want. If you choose Hibernate, you will have to briefly press the Power button on the computer to wake it after opening the lid.

I'm also having this exact problem after upgrading to windows 10.  

i did try changing those settings. Before it was to hiberante, but even tho with that i couldnt turn it back on, and its the same with just sleep. I also did try taking away the fast startup. 

Now i noticed that(no matter what settings) if i open my lid and let my laptop just stay like that, after few minutes i get the blue death screen and error message dpc_watchdog_violation

WHEN will a driver update be released?

I am disappointed by the communication about the old flagship of DELL. I hope it will be updated before 1 year during which Windows 10 is free!

Just learned that if I open up my laptop and let is sit for about 5 mins, the screen will turn on.  It however does not resume, it restarts.  All open windows are lost.  Lame

I agree with you!

I have the exact same problem. We know L702x and L502x aren't officially supported but I've seen older machines handle Win 10 with few issues.

Hope somebody figures out a solution.

Someone from tenforums posted a workaround:

http://www.tenforums.com/general-discussion/11776-unable-come-out-sleep-mode-3.html#post319585 

Basically, use Win 8 drivers for Intel graphics, Realtek audio, Accelerometer, and Dell QuickSet

why are they not supported anyways? I mean my windows runs perfectly fine and the hardware is more than good enough to run w10. After browsing around it seems that they have taken L702 out of the market. But why? When i was buying it, why didnt i get warned that the sale was only cause for some reason they are not even gonna support them anymore.

..Exactly !!!!!!!  I own DELL xps 17 as well, and i was very disappointed with support of company DELL for this product, for this laptop.  This notebook cost me over € 1000 and the support???? Is like for some kind of 100e box. Point???  This is not a nice advertisement for Dell. Let see, what"s gonna happen..We customers, as they customers needs support and not the ignorance.