Default [HELP] Hardware or update problem??

Hi! recently I made a backup of my stock rom, i´m always on stock rom slot with root, second launcher, xposed and google apps, but installing with apk files.

Today when i was viewing a video on youtube apk, it start freezing and then screen turned off. The physical buttons do not works. But i can turn off and then turn on the kindle, but when starting showing my icons on desktop, it started freezing again and then turning screen off. I don´t know whats happening.

So i entered to safestrap and i make a backup and then wipe data/cache/devilk cache.

Then, when is booted, i configured everything and then i opened a doc file and again screen was freezing and turning off.

Then i turned off and on again and when is booted again i manually put screen off with the power button.

Now everything go normal, so, my questions are:

a) Can i restore my safestrap backup?
b) Somebody know about this problem?
c) Is this an update problem?
d) Is this a graphic card problem?

Root persist because i recently installed es explorer and check on root button and work.
Sorry for my english.

Nexus 5