The POST happens every time you boot the computer. It is used to diagnose system-related problems and it contains two parts: the audible series of beeps, which alerts the operator to a problem, and the on-screen error code/message combination, which specifies the exact error encountered.
Typically, anything other than a single beep during this time indicates an error. The most common errors are a keyboard error and a CMOS low, or battery failure, error.
The error codes that you see on the screen fall into a particular range that can be associated with a specific component.
