Operating Systems/Dual booting

I setup a computer system running the following operating system:

1. win2000 professional
2. windows millennium
3. NT4 workstation and
4. NT4 server

They were quite up and running and I was happy with it. But when I switch on the computer system the following day, all other operating system has all disappeared except windows millennium. When I checked from “my computer”, the partitioned drives were all in place but the dual booting which comprises the four operating systems were not there. Where has the all gone to? Or how can I rectify the problem to enable me have my dual booting back. PLEASE HELP. AS IT COMPRISES OF FOUR OPERTING SYSTEM, DO YOU STILL CALL IT DUAL BOOTING OR FOURTH BOOTING?