iPhone 3G won't play ringtone?

[kitsune]

My iPhone 3G suddenly stopped playing the ringtone when people call me, and only vibrates. It is definitely not on silent mode, and is set to play on full volume regardless of the phone's volume setting. I am only using the phones standard ringtones and have tried a few of them, and they all play when I select them in the menu (so it's not a corrupted file), but I am always missing calls because they never actually play when I get called. What could be causing this, and is there a way I can fix it?

Thanks

[TattooFondue]

Try another ringtone, the ringtone file may be corrupted.