Many of you might have done this mistake, or no option left like in my client usually happen in every six month, it force you to change apps password via sqlplus. Now what application login will stop working, isn't it. Yes !!
Do this :
1. Change to old apps password via sqlplus;
SQL> Alter user apps identified by oldappspasswd;
2. Run autoconfig with this password in all tiers.
3. Restore customizations if any.
4. Start all services and you all set to login to your apps frontend login.
Hope this helps you all.
Keep Troubleshooting !!!