MY WINDOWS XP SYSTEM WILL NOT BOOT!
(OR MY SYSTEM IS UNUSUALLY SLOW)*
Last updated 09/06/2007

First, if you updated or replaced your motherboard, a common symptom when booting is an INACCESSIBLE_BOOT_DEVICE error.  See the "external link" below for troubleshooting in that case. 

If you have not done anything different to the motherboard, see if you can trace the error to recently-added hardware, especially USB devices.  Check your BIOS setup for a BOOT FROM USB option, and disable that if it is enabled. 

If there is no USB BOOT option, or it is disabled, you may have a legitimate problem with your hard drive - even the smallest bad "sector" on the hard drive can cause this problem.   IF YOU INSTALLED WINDOWS XP FROM A "RETAIL" CD AND HAVE ACCESS TO THE CD-ROM, you can do a recovery console repair below.  IF YOU HAVE A STORE-BOUGHT [OEM] COMPUTER, LIKE DELL, GATEWAY, ETC., DO NOT USE THIS PROCEDURE! YOU SHOULD BE ABLE TO USE THE NTFS4DOS PROCEDURE BELOW.

• PLACE THE WINDOWS XP CD IN YOUR CD-ROM DRIVE

• START OR RESTART YOUR COMPUTER.

• WHEN PROMPTED, PRESS ANY KEY TO BOOT FROM THE CD.

• LET THE CD LOAD, AS IF YOU ARE GOING TO INSTALL XP AGAIN.

• WHEN YOU GET TO THE "WELCOME TO SETUP" SCREEN, CHOOSE TO "REPAIR WINDOWS XP USING THE RECOVERY CONSOLE"

• AT THE RECOVERY CONSOLE, TYPE CHKDSK C: /F.  PRESS ENTER TO BEGIN THE CHECK-AND-REPAIR PROCESS.  IT MAY TAKE A WHILE; BE PATIENT!

• ONCE THE REPAIR PROCESS IS COMPLETE, IT WILL SHOW YOU A COUNT OF FILES, DIRECTORIES, BAD SECTORS, ETC.  AT THIS POINT, YOU MAY REMOVE THE WINDOWS XP CD-ROM.

• TYPE EXIT TO END THE RECOVERY CONSOLE SESSION AND REBOOT YOUR COMPUTER. WINDOWS XP SHOULD STARTUP NORMALLY.

IF YOU DO NOT HAVE ACCESS TO A WINDOWS XP CD, YOU CAN PERFORM THE CHKDSK PROCEDURE BY USING THE FREEWARE APPLICATION NTFS4DOS.

• DOWNLOAD NTFS4DOS FROM THE LINK ABOVE, AND USE IT TO CREATE A BOOT FLOPPY [YOU OBVIOUSLY MAY HAVE TO DO THIS FROM A SECOND PC IF THE FIRST ONE IS NOT BOOTABLE!]

• START OR RESTART THE AFFECTED COMPUTER WITH THE NTFS4DOS FLOPPY INSERTED.

• AGREE TO THE LICENSE AND YOU SHOULD BE SHOWN AN A:\> PROMPT. 

• IN SOME CASES, THE SYSTEM WILL CHECK DRIVE C: AND MAKE REPAIRS RIGHT AWAY.  IF CHANGES ARE MADE, REMOVE THE FLOPPY AND REBOOT YOUR SYSTEM; WINDOWS XP SHOULD BOOT NORMALLY.

• IF THE NTFS4DOS PROGRAM DOES NOT AUTOMATICALLY REPAIR YOUR DRIVE, TYPE NTFSCHK, AND PRESS ENTER.  YOUR BOOT DRIVE WILL BE CHECKED AND REPAIRED.

• ONCE FINISHED, THE CHECK-AND-REPAIR PROCEDURE WILL SHOW THE COUNT OF TOTAL FILES, DIRECTORIES, BAD SECTORS, ETC.  REMOVE THE FLOPPY DISK AND REBOOT YOUR COMPUTER; WINDOWS XP SHOULD BOOT NORMALLY.

* NOTE THE ABOVE PROCEDURES CAN ALSO HELP IF YOU EXPERIENCE YOUR SYSTEM SLOWING DOWN, OR NOTICE THAT THE HARD DRIVE LIGHT ON MORE THAN USUAL, YOU MAY HAVE BAD SECTORS ON YOUR HARD DRIVE THAT XP IS TRYING TO READ, BUT CANNOT.

Here's an external resource on MOVING WINDOWS XP...
CLICK HERE