Dell M90 manuals:

http://www.dell.com/support/home/us/...on-m90/manuals

Screen:

https://www.laptopscreen.com/English...PRECISION~M90/

Sample How-To video:

https://www.youtube.com/watch?v=Uj80suVoTCg


Moving the screen on its hinges to test for a bad connection may or may not work. I would not use that as a definitive indicator of the connection health.