When you try to repair your computer, it is important to know the startup or boot process, that is, when you hit the power button on your computer, your pc perfomrs a number of tasks before you can see the log-in screen. Since the boot sequence is somewhat complicated, let's have a look at them one after another in the following:
1. First your computer performs the POST, Power On Self Test. Beeps can be heard during the testing. This process tests the amount of physical memory and the other hardware components present. You can usually monitor this as it runs each test. After that is complete, the system will run POST for any device that has a BIOS, Basic Input-Output System. An AGP has its own BIOS, as do some network cards and various other devices.
2. Once the POST is complete and the BIOS is sure that everything is working fine, it will then attempt to read the MBR, Master Boot Record. This is the first sector of the first hard drive which is called the Master or HD0. When the MBR takes over, it means that Windows is now in control.
3. The MBR then looks at the BOOT SECTOR which is the first sector of the active partition. That is where NTLDR is located. NTLDR is the BOOT LOADER for Windows XP and it will allow memory addressing, initiate the file system, read the boot.ini, and load the boot menu. NTLDR has to be in the root of the active partition as do NTDETECT.COM, BOOT.INI, BOOTSECT.DOS if you have multi-OS booting, and NTBOOTDD.SYS if you have SCSI adapters.
4. Once XP is selected from the Boot Menu, NTLDR will run NTDETECT.COM, BOOT.INI, and BOOTSECT.DOS to get the proper OS selected and loaded. The system starts in 16-bit real mode and then moves into 32-bit protected mode.
5. NTLDR will then load NTOSKRNL.EXE and HAL.DLL which are windows XP files and must be found in %SystemRoot% System32.
6. Next, NTLDR reads the registry, chooses a hardware profile and authorizes device drivers, in that exact order.
7. Finally, NTOSKRNL.EXE takes over. It starts WINLOGON.EXE that in turn starts LSASS.EXE, which displays the Logon screen for you to log in.
