Check your power management settings to ensure that everything is set correctly. Also, go to the reliability monitor from the action center in Windows and see if there are any background apps regularly crashing. Some Store apps can run tasks in the background, and these can cause problems.
Finally, to take a look at what applications /might/ be running in the background, go to PC settings > Notifications. You may have quite a few things installed, and not all of these will actually be /running/ in the background, but some might, and turning them off to see if any difference is made might help.
If all else fails to a Windows Refresh from the 'General' section of PC Settings.
Glad the OP's problem is solved. Rather than two threads with the same subject, I'll mention my issue here.
My new Surface Pro (not RT) sometimes doesn't sleep (or wake) correctly and ends up going through a full boot when I turn it back on - nothing previously running is still running; when I launch IE it says my session ended abnormally; etc. To be truthful, it wasn't on Windows 8 long enough for me to notice if it's an issue specific to Windows 8.1, as I upgraded to 8.1 RTM within an hour of buying the thing.
Amazingly, it did not do it today. The only thing I remember doing differently was selecting "Sleep" from the start button last night instead of just letting it fall asleep on its own.
After I upgrade to 8.1 RTM on my Surface RT. I have the same problem too. I just close the cover to let Surface sleep or press the sleep button sometimes it can't wake up but I still hear the sound from the Surface and it still vibrate when I press Windows button. So I have to turn it off and turn it on again.
Another problem when I turn it on I log in by typing password with touch cover but type I can log in with virtual keyboard. Does it sound weird?