If you press and hold down F8 when the computer next starts it will display a boot menu. At the bottom of this list should be an option not to automatically reboot if an error is detected.
Even if this option is not available, there is an option to boot your machine in Safe Mode. Use this and then you can perform some maintenance.
how far into windows is it getting? do you get to the black screen tht says loading windows 2000 at the bottom? do you get as far as the logon screen? anyhow, if you search support.microsoft.com for windows 2000 'restart' you will see this can be caused by many things, due to handy feature of w2k that 'restarts on system error' boy, they were pretty confident about that, weren't they? it will take a bit to troubleshoot but it is not hard. first you need to disable that 'feature' then you need to research the error you will see when it stops on system error instead of restarting... if you have lots of free defragged hd space? then it is pretty easy. you will need a windows 2000 pro installation cd. while finding it, ask self: did this ever work? is it an upgrade? did i add hardware or upgrade drivers. this is the most generic article i found. it will get you started, maybe all the way... Windows Restarts Continuously with Blue Screen http://support.microsoft.com/default.aspx?scid=kb;en-us;174630
If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.
2000Pro Continuous Rebooting at Startup