I'm facing this problem since months,.. replace motherboards,...sent to repair and got it back in bad shape. The last call DELL indicated they have problem with batch of motherboards where a file created to go to sleep is corrupted and they don't have a solution yet!
I hope it comes soon as removing the file, is get corrupted very fast again.
I decided just to set up my Notebook to go into hibernate mode when I close the lid, press the power button, or after 15/30 minutes of inactivity. Hibernate mode seems to work fine. With an SSD drive, it wakes out of hibernate mode pretty quickly (7 seconds or so), even with 16 gig of memory.
With sleep mode, I worry that any "work in process" will be lost if the battery goes dead - although sleep mode is supposed to go into hibernate mode and write everything to disk when the battery power gets too low.
Besides, if sleep mode keeps memory in a semi-powered-up state, then theoretically, hibernate mode takes less power as you don't need to keep a charge to memory.
I've also come to the conclusion that there is no perfect Notebook. There will always be trade-off between processing power, display, battery life, features (like touch screen, which the Mac Book Pro doesn't have), etc.
Finally 3 motherboards - and all internal other boards and plugs - and what I asked for from the beginning - a new power supply - and finally my machine since about Oct/Nov 2015 has been working FAULTLESSLY - dare I say - dare I mention DARE I even breathe those words.
Actually NOT quite - keyboard spacebar doesn't seem to put a space in at odd times - an external keyboard fixes that at present.
Yep - faultless - sleep, hibernate, whatever - 100% not even a blip.
Hmmm - was it the power supply - perhaps - the replacement motherboards aren't new but rebuilt zapped ones I believe - maybe they fixed whatever was shakey - who knows.
Fingers crossed that woes gone.
So this was the external power supply used to charge the notebook, and nothing internal or software related? So sleep works for you regardless of whether or not the notebook is running on AC power or battery power?
What solved the issue for me was upgrading to Windows 10. My guess is that the new drivers solved the issue - for me, anyway. It works great. Close the screen lid, and bam, the notebook goes into sleep mode. Open the screen, and bam, the system is where I had left it. Nice.
This simple fix worked for me, yet it will not wake from sleep when opening the lid, only when pressing the power button or touchpad. Good enough, its waking up so quickly, hoooooray 😉
I can confirm that enabling "USB Wake-Up Support" works. The computer needs a tap on the power button to wake, but does so immediately and responsively, unlike before.