How Do I set my computer to boot up from a button on my keyboard?
It depends on whether your BIOS supports it, look in the BIOS for a section called "wake on Keyboard" or similar and I think you need a suitable keyboard as well.
This all depends on the motherboard. A very few of them will respond to a hot key combination to start the boor process - either your board will or it won't. To set it up you have to enable the option at BIOS level at boot time.
on your mobo you might have a jumper that enables you to press any button on the keyboard and the pc will turn on, it also needs to be enabled in your bios though, as the other guys have said
check the manual for your mobo