The DHCP server may fail to start if the database becomes corrupt. An indication is an event in the Event Log like this:
Event ID: 1014 Source: DhcpServer Type: Error Description: The Jet database returned the following Error: -1022
To fix it, perform the following steps:
net stop dhcpserver%SYSTEMROOT%\system32\dhcp\dhcp.mdb with its backup from %SYSTEMROOT%\system32\dhcp\backup\jet\new\dhcp.mdbnet start dhcpserver
If this doesn't work, you may need to delete the entire %SYSTEMROOT%\system32\dhcp folder.