Seems your database is not running.
I'm not very familiar with Windows, but try starting the database.
There is a Tool under the oracle directory to do this.
Try looking here (Names might differ):
Under Start>Programs>Oracle - OraHome81> there is a Database Administration or Database Management directory and under that you will find a tool with a similar name.
This tool is used to start/stop (and do other stuff) to the database.
Good luck.
There