Video goes upside down and dulls after text input

This has happened three times. After I try to put text on sections I have already edited, the video within those sections starts behaving weirdly. First, sections of video start playing UPSIDE DOWN, and other sections appear as if there is a dull colour overlay. What might I have done to cause this?

I am also having trouble putting simple text over stills and video. There must be a simple way of doing this...adjusting size and location of text, moving it around the screen, adjusting time on the screen, and making changes. Where can I find a simple explanation of this, please?