iphone screen turns white but i can get it to show the home screen

I've been having an issue with my iphone that I have not been able to find a post about. My screen turns white and will start to display lines of horizontal colors in fast motion. In order to get it to show the home screen I have to hold the top button and the home button for a loooong time. As soon as it goes to sleep the white screen is back. It started happening last weekend, I made an appointment for the genius bar. I showed up on monday and the phone had not been acting up all day so there was nothing they could do. I wake up today, friday morning, and my phone has the white screen again. Sometimes when it's on white screen mode I can still hear the phone ring, other times it goes straight to voice mail. I can hear text messages arriving also. I can even see the white turn to gray when I hold the top button as if it is receiving a signal to shut off. I did a system restore, but it did nothing. Im afraid that apple is not going to fix my phone because I dropped it about two months ago and it has a slight dent on the top where the headphones go. I know that the dent has nothing to do with the white screen issue because this started last weekend. Has anyone else had this issue? and question #2 do u think apple will have a problem fixing/replacing my iphone if it has a dent?