While on the screen turns black or off for 15 seconds and comes back on.

Windows 8 especially and sometime Windows 10 may have a black screen during an update for over 15 minutes with no indication that anything is happening.

Try complete power down by holding the power key for 10 full seconds. Consider unplugging power for a few seconds after that as well.

Re-connect power, press power button to turn on the computer then if the screen goes blank, give it a half hour before looking for another solution... it may come back to you.

Ok try this, at boot up press F8, when the Menu comes up, choose Safe Mode, but this time instead of going to the desktop, choose System Restore, follow instructions, and when the Calender type window comes up, simply choose a time BEFORE, the time it went faulty. This should completely restore you to working again. As long as there are NO other problems.
support.microsoft.com/kb/306084 -

could be a loose ribbon.

you Screen has a Soildation problem take it to near by electrition he will resolidate your screen and it will then work fine..

Can you try, holding the Power Button and the Home Button for 15 seconds, the screen should turn off (well in this case since it seem like your phone is off, have someone text you to double check it's off), then turn your phone back on.

press and hold the power button, wait for computer to shut down... then wait 10-15 seconds and turn it back on.

It could be a bad backlight bulb.

there a problem with your phone memory, try adding an external card, if it has one. if you do have an external memory, try to remove it, and power-up your phone. if the problem persist it needs servicing.

The solder joints on the vertical output IC have cracked. This is a very common problem on those sets.