Your computer is pretty beefy and Mugen won't load stuff unless its in the select.def file. My guess is that a character is probably making your Mugen crash. I recommend you leave it running on attract/demo mode overnight and check in the morning the mugen.log file to see what's the last character that was unable to be loaded. Remove them from the select file and try again until it doesn't crash anymore. It's what I did and my Mugen doesn't crash anymore. My record is four days running it non-stop until I needed to use the computer (417 Characters, 427 stages all with music, 12gb total).