my grandson was playing on my phone, the screen is now black and i cant do anything , you can still ring it but cant answer it
Try holding down the home button and the sleep button at the same time for about 10 secs, not knowing what phone you use it's difficult to answer, if that doesn't work try this page.
https://www.google.co.uk/search?q=my+phone+has+just+gone+black&rlz=1C1CHIK_enGB517GB517&oq=my+phone+has+just+gone+black&aqs=chrome..69i57.115894j0j4&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8
This is a Simple Dialog Demo.