So it freezes during the loading screen? It sounds like you might have some corrupted files in the DLC (for whatever reason). I take it, you are not using any mods?
Try the following:
Go to your ME3 install folder (where the game itself is, not the saves), then go to ".\BioGame\DLC\". Find the subfolder called "DLC_EXP_Pack001" and delete it (or maybe rather move it to another folder, so it's gone from the ME3\BioGame\DLC\ directory). Now open Origin, right click on the ME3 Icon and select "View Game Details". In the following screen scroll down through the list of your DLC. Since yuo deleted the Leviathan folder, it may be that the Laviathan DLC now has the "Install" button on the right side of the list. If not, right click on Leviathan in the list and click "Repair". This should reinstall Leviathan from scratch and will hopefully resolve the problem with loading the map.
The reason to do it this way is because "Repair Game" will not necessarily repair your DLC and even if you choose the "Repir" option for the DLC directly, it may not actually re-install if there is a file already in place that passes all the checks. So deleting it first and then re-installing makes sure that you do get new and clean files from Origin.
Hope that helps and good luck.
Okay, finished, and.....
It keeps getting stuck on the "LOADING" part.