ntoskrnl problem when i attach a 2nd HD

Hi i have vista on one hard drive, xp sp2 on another and a 3rd i use for storage. Originally i had this set up and it worked fine, if i wanted to boot in vista i would change the HD boot order in cmos and same for xp. Then my xp HD failed after a year so i replaced with a new 250gb Maxtor and installed xp.

now when i try and boot xp i get,

Windows XP could not start because the following file is missing or corrupt:

windows\System32\Ntoskrnl.exe

Please re-install a copy of the above file.

I found that i could get round this by unplugging my HD containing vista and i no longer get this message. Ive tried having them both plugged in and using windows recovery console to replace this file but i still get it and have also tried bootcfg /rebuild but it says something about file system corrupt.

Can anyone help please? Many Thanks James.