It shuts off

Try changing the CPU processor and its heat sink with another known processor and heat sink but it has to be identical or same of its own processor fan.

it seems not to be a boot up error it is an windows start up error

might be the boot up files for windows are corrupt
solution:

1. if you have a registry backup you can restore it through recovery option with windows XP setup

2. better reinstall the operating system will fix the problem

seems your MBR is damage. you need to boot in the windows cd and enter in the recovery console.

To run the Recovery Console from the Windows XP startup disks or the Windows XP CD-ROM, follow these steps:
1.    Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.

Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted.
2.    When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
3.    If you have a dual-boot or multiple-boot computer, select the installation that you must access from the Recovery Console.
4.    When you are prompted, type the Administrator password. If the administrator password is blank, just press ENTER.
5.    At the command prompt, type this commands one at a time.

FIXMBR  C:
FIXBOOT  C:
COPY [CDDRIVE]:\I386\NTLDR  C:\
COPY [CDDRIVE]:\I386\NTDETECT.COM  C:\
BOOTCFG  /rebuild


6.    To exit the Recovery Console and restart the computer, type exit at the command prompt, and then press ENTER.

no warranty...you use on your own risk :)