Did you log in as administrator? If not, then you must explicitly name the owner of the NT services.

Do the following:

1. Open the "Services" dialog box from the NT Control Panel.

2. Click on the OracleService then click the "Startup..." button.

3. Change the "Log on as:" information to "This Account: " plus the appropriate password where username> = the person who created the services.

4. Repeat steps 2 & 3 for the OracleStart service.

In some cases the ORA-3113 occurs even if you are logged on as the NT administrator. In this case = Administrator.