Phone went Blanks
I had my phone plug into speakers at work, unplugged it travel home, rest it down and shut off and wont come back on.
iPhone 4, iOS 5.1
Basic troubleshooting steps clearly outlined in the User Guide are restart, reset, restore from backup, restore as new device.
If you have gone through ALL the above steps and are still having problems, then you'll need to bring your phone into Apple for evaluation.