This is only quirk I've experienced with my X51v since getting it a few weeks ago. What happens is that for some reason I loose functionality in one place, but works fine in another, and then functions as expected after a soft reset?
For example:
I keep losing the ability to access "Power" through Start-->Settings-->Systm but can access it fine from Start-->Home. Same goes for Start-->Settings-->Connections-->Dell WLAN Utility. I've been using these two things quite a bit as I learn my Ax. A soft reset cures this for a few days and then it starts again. It has happened when both the unit was configured as-is from Dell with no media cards, and since I've loaded a couple of things on it.