First thing to do is to save off the Data while you can because you will need to reformat and reinstall Windows again.Once you have saved the Data, put the HDD back into the other Computer and boot into your Win 2000 Disk. Once there Delete the Partition, then reset it as C: Drive and Format it. Install Windows 2000, Anti Virus, and all Drivers needed, before going onto the Net, to protect it. After that go to Windows Update and download all Updates, then update your Anti Virus and fit Anti Malware and update those.Putting a HDD into another Computer can be very risky if a Virus is present on it, as the Virus can also infect the other Computer. I would always run Anti Virus and Malware on it before ever opening it up in any way.