Boot...as in an operating system other than standard disk basic? FYI, disk basic is in ROM on the adapter cartridge you plugged into the side of the computer. Unless you replace this ROM, the computer won't "boot" or automatically run any programs on that disk at power-on or reset.
That said, though, should you be interested in booting another OS, type "DOS".
How do you have it connected? Is the cartridge connected to the ribbon cable connected to the drive? Is the drive plugged in and powered on? These probably seem like silly ideas, but just thought I should ask.
I can't remember if some CoCo drives have fuses or circuit breakers. You might want to look on the back for something like that.