Do you have a Windows Installation disk?
If you do, the information at the following link may help:http://www.kellys-korner-xp.com/xp_haldll_missing.htm
If not, try to boot to safe mode with command prompt.
To boot to safe mode menu start tapping F8 as soon as you power on the computer and before the Windows splash screen comes on.
Log on to your computer with an administrator account or with an account that has administrator credentials.
Type the following command at a command prompt, and then press ENTER:
4.Follow the instructions that appear on the screen to restore your computer to an earlier state.