If you find that MC1 or MC2 boots fully, but the other only boots to the splash screen, then this could be caused by both MC's having the same identification.
The identification of the MC is controlled from the Home - Preferences - General page. Go to this page on the MC that has booted. At the bottom of the page will be a picture of the surface. There will be a red box covering either the left or the right bays.
For MC1 (left bay) the picture should look like this;
For MC2 (right bay) the picture should look like this;
If the screen is incorrect, then using the mouse cursor click on the other bay and the red box will move. Shut the console down and using the recessed reset switches on the master module, put that MC into reset. Re power the console and the other MC will now boot. Check the Home - Preferences - General page and move the red box to the other bay if necessary. Once this is done, take the other MC out of reset. The console should now be operating normally.