Help with latitude d600 shell32.dll corrupted, computer won't boot?

Hello, I have had this computer for years, never gave any trouble until now. I turned it on the other day and after the message that windows xp is loading instead of the pword box I get a warning saying "STOP: c0000221 {bad image cheksum} The image shell32.dll is possibly corrupt. The header checksum does not match the computed checksum" and I realized that I don't have the repair disk anymore. I managed to get a program called barts pe and I am able to see the registry and even files on the hard drive. However all my efforts on copying the shell32.dll with a external hard drive to the computer hard drive didn't work. Please tell me how I can fix this, and if maybe I didn't erase and replaced the right shell32.dll (is there more than one?)or if I can fix it with the regedit command.