BSOD: inaccessible _boot_device HELP! Win 2000

Ran the Reg Mechanic on 3 systems (did not purchase yet just the first run)operating on Win 2000 today. Two it worked fine on - the third - well now is getting the BSOD stating inaccessible_boot_device. I cannot get into windows in safe/safe networking/ or last good conf. now. I did manage once to get in via last good conf and when I attempted to do anything - nothing would open-the whole thing locked up! So I shut down and upon it trying to boot back up I got windows\system32\config\system error??
Anyone have any clue as what happened or how to fix this? This is on a computer at work and we were doing reg clean on it because it is a pooch and kept giving the error that virtual memory was too low. I do not have the original CDs to reinstall Windows. Any pointers would be helpful - I am still learning so please use laymens terms! Thanks