I am real sorry to hear you think your phone is toast. i missed where you went through the trouble shooting of it. Have you really exhausted all the possibilities here, do you think?
Won't they give you a new phone for $100? If so, if you saved that up, wouldn't they want the old phone back too?
I saw somewhere you said you think something might be loose inside?
If you really have tried everything the guys here can think of, maybe you should take a look at this?
replace evo 4g screen - YouTube
It is talking about replacing the screen on the evo. I know you say it isn't broken, but they take about everything loose in the video. maybe you could take it apart with the instructions and find something loose or broken and fix it?