Goto command prompt.

then type

C:\>svrmgrl

Oracle Server Manager Release 3.1.5.0.0 - Production

(c) Copyright 1997, Oracle Corporation. All Rights Reserved.

Oracle8i Release 8.1.5.0.0 - Production
With the Java option
PL/SQL Release 8.1.5.0.0 - Production

SVRMGR> connect internal
Connected.
SVRMGR>shutdown normal;

This will shutdown the database properly.

Paresh