Folow this logic :

set ORACLE_SID=demo

E:\orant\bin\oradim80 -new -sid demo -intpwd manager -startmode auto -pfile E:\orant\database\initDEMO.ora

E:\orant\bin\oradim80 -startup -sid demo -starttype srvc -usrpwd manager -pfile E:\orant\database\initDEMO.ora

U do this in a dos window on the server

Good luck