I got on Origin today and saw that it was prompting me to preorder and preload Mass Effect 3. . After pre-ordering it, I went to my game library to preload it, but the "preload" button is disabled! Why would this be? Does it have something to do with already having the demo downloaded?
For any origin game, the following steps have been shown to help with getting the preload work.
Do note, that some people experienced this more when they ordered the game from the site rather than the client. Again, giving it a minute and then restarting Origin is probably your best bet.
Now, ME3 in particular has had some other issues. As quoted from a Bioware Representative:
This may occur with other games in the future as well, so it is something to note. They throttle the number of people downloading if their servers get to overloaded, so keep that in mind.
Also, do note that each game has a set release schedule that may vary based on the region in which you live, and you may not be able to download the game yet. For ME 3, the schedule is here, however other games will likely have their schedule available via the Origin support website.
If you continue to have issues, you can always contact EA support.