I know this is a very old post but I had this happen to my CAS calc and fixed it so thought I may as well chip in.
Tried everything mentioned in the thread, took the battery out for >10mins, formatted and updated to latest OS, and gave it a few good hits in case there were any loose connections.
None of these worked so I took it apart. Noticed there was a small speck of oxidization or something on the connection from the screen to the main board. got rid of the speck and now everything is back to normal, no more flipped screen.

Not sure if there was a connection between the two but worth checking out if you're having this issue.