Solution here: http://blogs.oracle.com/middleware/2010/05/weblogic_not_reading_bootproperties_1111x.html
Just go to user_domains/MYDOMAIN where MYDOMAIN is the domain that you want to start.
Goto Servers/SERVER where SERVER is the SERVER that you want to start.
Create, if does not exist a security directory
On the security directory create a file named boot.properties with the following entries:
username=
password=
Just put your un-encripted password. At startup the password will be encrypted.
More Here
Courtesy:http://primalcortex.wordpress.com/2010/11/04/weblogic-application-server-startup-without-asking-for-password/