hi there, welcome to Ozzu.
You probably have a boot up failure because of a missing boot.ini. When Boot.ini is missing or curropted, you can no longer boot up your PC. it will show you a missing boot.ini and then it will display
"Windows could not start because the following file is missing or corrupt:
<Windows root>\system32\hal.dll
Please reinstall a copy of the above file.
You dont have to reinstall hal.dll (Hardware Abstraction Layer). your hal is just okay. its your boot.ini which is casuing to fail boot up. all you have to do is rebuild your boot.ini using Windows XP installation CD
Insert the Microsoft Windows XP CD into the computer. Note: If you have a system recovery CD or restore CD these steps will likely not work for your computer.
Reboot the computer with the CD and press any key when prompted to press any key to boot from the CD.
Once in the Microsoft Setup menu press R to open the recovery console.
Select the operating system you wish to use; if you only have Windows XP on the computer you will only have one prompt.
Once prompted for the password enter the Admin password and press enter.
Once at the command prompt type 'bootcfg /rebuild' to start the rebuild process.
The rebuild process will step you through a number of steps depending upon how many operating systems you have on the computer and how the computer is setup. Below is a listing of the common steps you are likely going to encounter.
* Prompt for the identified versions of Windows installed. When you receive this prompt press Y if the bootcfg command properly identified each of the Windows operating systems installed on the computer. It is important to realize this command will only detect Windows XP, Windows 2000, and Windows NT installations.
* Prompt to enter the load identifier. This is the name of the operating system for the boot.ini. For example, Microsoft Windows XP Home users would enter "Microsoft Windows XP Home edition".
* Prompt to Enter OS load options. When this prompt is received type /fastdetect to automatically detect the available options.
Once you have completed all the available options in the rebuild and are back at the prompt type exit to reboot the computer.
You may find this site helpful
http://support.microsoft.com/kb/330184