This is an odd one. It doesn't look like any screen failure I've seen before so I'm afraid it's not a slam dunk to just say, "replace the screen". The half circle at the top somewhat resembles a cracked screen; if you shine a flashlight on it and look at it through a magnifying glass you may or may not be able to see an actual crack in the glass. If you do see a crack then I'd say it's a strong indication of a broken screen, but it's not necessarily conclusive if you can't.
I know it sounds wishy washy, but there's no strong indication of a screen problem, but on the other hand there's not that much else that it could be. Can you power down the phone and turn it back on again? If so, does it come back to the same screen immediately or is there anything else displayed? Does the phone give indications of working "normally" other than the fact that you can't see anything on the screen? Does it respond when you call or text it from another phone? Does it connect to a computer? Give you an indication when you plug it into a charger?
I'd say if it was mine I'd probably try and open up the back and unplug the battery for a while then plug it back in and see if anything changes when you try to power it up. In the absence of any other progress, replacing the screen is really all you've got left at that point.
Yeah, I understand about these expensive screens; I felt bad telling my niece that $185 was the cheapest I could find a screen for her phone when she broke it.
At this point it really does sound like the screen is toast; to all appearances everything else is working. I'd say the one thing you can do before you break down and order a replacement screen would be to open the phone up and try reseating the display connector. Follow the screen replacement guide through Step 14 and unplug the battery, then skip to Step 18 and unplug the screen connector. I don't honestly think you're going to find anything, but for the sake of covering all the bases, check both sides of the connector with a bright light and a magnifying glass for any bent or broken pins and check the length of the cable for any sign of tears or damage. Assuming everything looks good there, clean the connectors with 90% or higher concentration isopropyl (rubbing) alcohol, let them dry for a minute then plug everything back together and retest.
Although it's theoretically possible for the connector to come loose due to drops and jars, in practice those connectors are held down pretty securely and almost never pop off.
At this point, assuming the problem is still there, there are only two valid possibilities; one, the screen is dead, or two, the motherboard is damaged and the graphics system has failed. Since you can't really do anything about the second scenario, you're left with the first of replacing the screen as your only real shot at fixing the phone.
Most of the screen vendors will let you return the screen as long as it hasn't been installed. Which means when you get the screen, open up the phone and go to the point of disconnecting the display as the instructions I gave you earlier show, then plug the replacement screen in without attempting to mount it or even remove the original screen. You should get a picture on the replacement to verify that it's going to solve the problem. If against all odds the new display shows the yellow screen then you can put the new screen back in the box and return it.
That's the best advice I can suggest for you right now, Kim. Hopefully that will help you get your friend fixed up without losing any data on the phone. Let us know how it all turns out!