After I started the Websphere Application Server version 6.0.
I got the following error in the console :
com.ibm.websphere.management.exception.AdminException: ADMU7704E: Failed while trying to start the Windows Service associated with server: server1;
After digging for awhile in the problem, I could solve by :
1. Going to the services list in Windows (Administrative Tools -> Services).
2. Selecting the service for WebSphere Application Server.
3. Opening the service's properties and selecting the startup type to "Disabled".