OK, I don't know what the issue was, but I deleted my display drivers, unplugged the 2nd monitor, shut down and restarted and mame now loads on the correct monitor.
Sorry to res this thread, but I am having a simular issue.
I have 2 monitors (a marquee screen and game screen), I found the displays by using the verbose command. I edited the .ini file but it doesn't change anything.
In my display properties it lists the monitor I want to display the game on as screen 1. But both mame and BigBox see it as screen 2.
I am editing the mame.ini file in the main mame diretory with exe file.
Any ideas?