Looped Reboot after SP2 installation?

Hi,

One of our XP Pro computers didn’t have SP2 installed, and as part of the “housekeeping” we tried to install SP2 on it. All went well until it rebooted. When it reaches the “Windows XP” logo and progress bar, it just goes right back to POST constantly in a loop until we switch it off.

We reformed it with just WinXP on it as a short term fix, but can anyone suggest a reason and/or fix as to why this machine reacted this way?