What do the red blinking LED codes on the power button mean?

Red blinking LED codes indicate specific hardware failures. For example, 5 blinks means a pre-video memory error, 6 blinks indicates a pre-video graphics error, 7 blinks signals a system board failure (ROM), and 9 blinks means the system powers on but is unable to boot. Each pattern consists of a set number of blinks per second followed by a 2-second pause. (Page 3)