Why will the mx 900 not turn on even with new batteries

You should set up the remote control with the set-up codes to your device brand.
Check the remote control for its infrared emission. Check it with fresh batteries. If you wish to get more details about how to check a remote control, please visit this site. One among the posts has details about it. Surf the site in "Mosaic" or "Magazine" view. It will make surf easier.
http://electronicshelponline.blogspot.com/
If remote control is found OK, and have infrared emission, set it up with your device by using the set-up codes.
If you wish to get more details; check the sites linked here. It has set-up code list & set-up procedure to many popular brand remote controls. Common codes used for devices too are given, in the order of device brand name list in alphabetical order. Do a search by type in the brand name of your device, at its search box, and press "Enter". Or, pull up older posts.
http://remotesearch.blogspot.com/
http://electrohelponline.blogspot.com/