I assume you have the version which loads it's game from a cd.
Normally, the cd should be in the drive before you power the system, but that's likely not your problem.
The megatouch XL loads it's dos from a romdisk on it's io board If you open the pc compartment, the io board is the top board in it. The pc board has a riser card in it's AT slot that allows the io board to be mounted horizontally as well.
Sometimes, the pcb edge connectors make bad contacts. You can degrease them with a pencil remover. You could try to wipe them clean with some desinfection alcohol as well. The io board also has a jumper to enable the flash rom, but I see no reason why someone would have switched that. Besides the rom bootdisk, the io board also is the sound card. It contains a 32K memory mapped Non Volatile Memory that is used to store the settings and the high scores. The eprom on the board is a bios extension that enables the flash drive. The io board also provides the interface with the coin acceptor and the test and calibrate buttons. Last but not least, it contains the Dallas protection dongle that should match the program version in order for that to run.
So, if your megatouch comes up with a boot failure, it can't boot from it's flash romdisk. So, the first thing to check is the io board and the riser card.