Oracle Database Express Edition (XE)

I have installed Oracle 10gXE in Windows XP SP3

which is giving me the following error when trying to connect to the instance XE. Ora-12514.

Looking for information about this error, I managed to access the database instance after performing the following instructions.

sqlplus / nolog
conn sys / as sysdba skf
connected to idle instance (or something)
startup nomount
----
immediate shutdown
startup mount
---- mount the database
database recovery
----
alter database open
conn sys / skf as sysdba @ xe
connected

this gave me the opportunity to create a backup of the database. But again, reboot the OS again show the same error. Reinstall Oracle 10gXE to see if correcting the error, but no.

I was doing tests on a virtual machine, and I realized that running the status of the listener (lsnrctl status), the summary of services does not appear XE instance.

What else I can do?
The windows firewall is disabled, the PC is installed the Symantec End Point Protection with the firewall disabled.

thanks