If the hard reset didn't produce an apple logo; and the device isn't showing up in iTunes; there is a chance the hardware may need service.
Try doing a hard reset on the phone;
1. Hold Home and Sleep/Wake buttons at the same time;
2. Wait for the Apple logo to appear
3. Let go of the buttons when you see Apple on the screen
iTunes doesn't recognize the device
Have you tried different usb ports on the computer? or a different cord possibly?
Also see the below articles:
For Mac: http://support.apple.com/kb/HT1747