Why is my Microsoft Lumia 540 having a black screen?

[Tumbryn B]

My Microsoft Lumia 540 suddenly started displaying no icons on the screen. its running Windows 8.1 mobile and previously had no problems.
i can receive calls but am unable to make calls. i can view some notifications which are numbers 5B04B775356B4...
Any ideas on how to get my phone working well again?
Thanks