start sqlplus as sys (like you already did) and start the installtion.
D: cd \downloads\apex4.0\apex_4.0\apex
start SQLPlus in cmd
Then give SYS user password
sqlplus /nolog CONNECT SYS as SYSDBA
Go get coffee or tea.
@apexins SYSAUX SYSAUX TEMP /i/
Set INTERNAL workspace ADMIN user password