If the database has been corrupted and you do not have a workable backup copy, you have to delete the database, and then create a new one.
When you check DHCP Manager, the scope still exists because the Registry holds the information on the address range of the scope, including a bitmap of the addresses in use. You need to reconcile the DHCP database to add database entries for the existing leases in the address bitmask. As clients renew, they are matched with these leases, and eventually the database is once again complete.
Although it is not required, you can force clients to renew their leases in order to update the DHCP database as quickly as possible. From the Command Prompt of the client computer, type the ipconfig/renew command.