What it is for if you press and hold down the power button on a mac pro? The light flash really fast and make a really loud beep. I know this is use for Firmware upgrade, but I try to restore a Firmware update but couldn't. I try holding the power button while the computer start up see what it for but I get a blank screen afterward. Is this going to screw up my Computer? I force shutdown already and already went back to Mac OS X just fine.