My DHCP server is down! Urgent!

In Windows 2000 server, when fresh installing, I set up DHCP service for machines in our Intranet. Now the DHCP service is down! In Services, I can start the service manually, but it will stop automatically in a few minutes. And in DHCP console, it always show that “Cannot find the DHCP Server”. How can I recover the DHCP service? (I?ve tried uninstall and reinstall the service in Control Panel, Add/Remove Windows components, but still remain the same)