The first thing to do would be to clear the cache and data form the camera app and hope that it's a software glitch. Iif this doesn't work, the next stage is a full facory reset. I wouldn't be over-hopeful about this, but it would be part of any repair, so you won't lose anything by giving it a go yourself. Don't forget to back up your data, and also remove any sd card as the process sometimes formats them.
If the problem persists, it sounds like a hardware fault and will be a repair job, I'm afraid.
