Power-on self test

The POST, in most computers, is a self-test^[1] that checks the OS(s) available and boots from the OS selected. POST stands for Power On Self Test.^[2] Computers that have an operating system perform a POST before loading the OS, and many imbedded systems also do a POST.

A POST usually checks the crucial, files, folders, and components. Once the POST is completed, a selected OS will take control and finish the startup process.^[3]

If the POST fails, usually a BSOD displays (Blue Screen of Death, most commonly) and offers recovery options such as safe mode.^[4]

Other tools

LKGC (Last Known Good Configuration) reverts to the last non-problematic, successful bootup.^[5] It is similar to System Restore, but its primary function is to allow the user to use the computer normally, unlike System Restore, which does not guarantee a fix. Also, LKGC is unrevertable, unless you successfully bootup again.^[6]

System Restore works by allowing the user to open a wizard, then select a "restore point". The user must restart for the point to take effect, but the system will start as normal.^[7]

System Repair is typically found on the hard disk of your computer^[8] and contains options that can be used to fix the system. However, in serious cases, the OS may need to be reinstalled.^[9]