Recently installed Windows 7 64 bit on my main hdd (had previously had it installed as 32 bit). Now my back-up drive gives me this error. The back up drive does not have windows installed on it, and is not a boot drive. But when it is connected I get this message: "Windows root system32 ntoskrnl exe missing or corrupt." In order to boot on my main drive, I have to disconnect the back up drive.
I don't understand where to reinstall the missing file - if I put it in the Windows 7 files, won't that mess up my main drive?
It sounds like the backup drive is taking place of the main drive and will not boot that way. You need to make sure the backup drive is seen as the secondary drive not the primary. You can check this in bios or when the computer boots and shows you what HD's it has installed and what order they are in.