Why won't it power off when I close the screen?

My unit charges and when I swing the screen open it powers up and records fine but it won't power off when I close the screen like it normally did. If I take the battery out I can restart the process but if I forget it naturally drains down. I use it onboard to record our racecar so sometimes we get busy. I'm thinking a switch or sensor needs cleaning but nervous about taking it apart.