My Windows 2000 (optiplex) reinstall continuously. Is show Windows 2000 screen and restarts. I don't know if it is due to:

- the installation of a software

- a virus

- an antivirus update

 -or a hw problem.

I want to reinstall, but over the actual system, without formatting. Must I install it from the Reinstalling CD booting from it? I think it is the only way to boot, to recognize the 40 Gb HD and to launch the installation.

Can someone help me?

Thanks