Computer will not boot up. Help needed : )

Hi all. I have a problem with my Dell 4500, with XP. I turned it on, before it booted up i turned it off. Now when i turn it on it says "windows could not start because the following file is missing or corrupt"   \windows\system32\config\system              it says  "repair this file by starting windows setup CD and select R in the setup menu.  I have run the cd but i have no idea what to do next. Any help or advice would be great.

Thanks

BR

Steve