How to rectify this?

I have Canon 590IS camera. Recently, when I took photos at night where there is light-source directly behind the image, it shows a horizontal line on the screen but when I uploaded to my computer, it was not there. I also took a video and that horizontal line is there is the video too. Is this a problem with lens? please help me. how to upload video as a sample in this site.

Is the horizontal line in the video file, or only displayed on the camera? Is the line straight and thin, soft and big, describe it.