See THIS from Microsoft on how to fix it.
Hi, I have problem with my windows XP home edition - sps3 My last known it was running windows update when completed updating I shut down and the next morning when I turned on I had a message: Window could not start because the following file is missingor corrupt:   \system32\hal.dll.    Please re-intall a copy of the above file. I google searched and found utube and it doesn't work ([URL] My computer doesn't boot up like in that utube. Does any one out there know how to do it properly? Please help me.  Thank you.
Window could not start. Hal.dll is missing or corrupt