My 16GB 1st gen iphone has fallen on the floor from a 7 feet high desk. The screen is intact ( or at least appear to be so ) , but the phone does NOT power up. Not even if I connect it to the PC , nor is recognized by Itunes. I opened up the iphone to see if there was any apparent sign of a problem, but nothing. I know that the question may be too general, but what may have happened due to the fall ??!?!? And how should I troubleshoot the situation to determine which part is failing ??!?!