If you forgot your Oracle XE 'system' account password, follow these steps to reset. In fact, I forgot and reset it just now.
Windows: Open any DOS window and do the following.
C:\set ORACLE_SID=XE (or your service id)
C:\sqlplus / as sysdba
You should see SQL> prompt with DBA privileges. Next, issue sQL command to alter the passwords for SYSTEM and SYS accounts.
SQL> alter user system identified by
SQL> alter user sys identified by
You need to reset password for both SYSTEM and SYS accounts.