I removed a hard disk from one of my computers (let's call it PC 'A') and installed on another computer (PC 'B'). The hard disk was the C:\ drive on PC 'A' i.e the OS was installed on it. I installed it as a slave on PC 'B' and it works fine. My question is: when I return the hard disk to PC 'A' will it still work fine i.e booting et al? Or should I prepare myself to install a fresh copy of Windows? I didn't mess with anything (regitry, system files), I just accessed music and games which were on the drive and added a few more files. Thanks P.S. I am guilty of deleting a "very important" system file called "NTDETECT" on the hard disk. Thing was my antivirus reported that there was a virus by the same name on my system. I've already downloaded a bootdisk from the internet and made a bootable floppy disk in case booting doesn't take off.