Here's a quick plan of how you can turn on your whole cabinet with the push of one button.
Note: Not shown in this file, but for the actual "On" button, I usually take apart the PC faceplate, and extend the wiring that goes from the start button to a new button that I locate somewhere out of the way on the cabinet (like on the top, or on the bottom of the CP). Another helpful item is to also extend the PC's "reset" button so that if mame or your pc ever hangs somewhere, you can easily reset the PC without opening up the cabinet....