A restore may help your iphone - it is one of the troubleshooting steps. Page 141 of the manual:
"If you restore, the latest version of iPhone software is reinstalled, default settings are
restored, and data stored on iPhone is deleted, including downloaded applications,
songs, videos, contacts, photos, calendar information, and any other data. In iTunes,
you can also restore from a backup without deleting data stored on iPhone.
Deleted data is no longer accessible via the iPhone user interface, but is not
permanently erased from your iPhone until it is overwritten by new data. For
information about permanently erasing all content and settings, see “Resetting
iPhone” on page 109. "
http://manuals.info.apple.com/enUS/iPhone_UserGuide.pdf
I gave you the link to the Apple article to determine hardware failure earlier. If those steps or a reset, restore don't work then you need to call or visit Apple for a replacement.
