Hi,

1. When u create the SID, u need not give the startmode option. By default it will be set as automatic.
Even if it is set as manual, go to Control Panel->Services and change it to Automatic.

2. For performing the STARTUP and SHUTDOWN operations your user should have the SYSDBA privileges.
If you want to perform all these things by connected as the SYS user then you should connect like,

connect sys/pwd as sysdba.

Vijay.