Agreed. The ideal order of debugging Microsoft device (here, it is the Windows Phone 8) related problems is (in order from the least to greatest hassle and effort):
1. First, try to simply restart your phone. Just press the power button until you are prompted to slide down the screen to turn your phone off.
2. Second, if restarting doesn't work, do a soft reset by pressing the volume down button and the power button together until your phone turns off and vibrates.
3. Third, if soft reset doesn't work, then a hard reset can be tried. This will erase all your data. Go to Settings > about > reset your phone. Be sure to back "everything" up under Settings > backup FIRST.
4. If all of the above didn't work and you're using a Lumia, you may have some luck with the Nokia Software Recovery tool... but this is mainly intended for devices that won't turn on completely. If you're not using a Lumia, then bring your phone to a service center.
5. Have your phone replaced.
To answer the question in the first post, I encountered the same problem with my L1020, but a simple restart fixed the problem.