Check Web Server is Up :

Oracle Applications DBA Field Guide

Check in browser http://hostname.domainname:port where hostname.domain_name is Machine Name on which Web Server is running.

Check Jserv is Up :

Oracle Applications DBA Field Guide

Check if you can access OAM (Oracle Application Manager) page. http://hostname.domainname:port_number/servlets/weboam/oam/oamLogin If you can't access login screen for OAM, check logs.

Check mod_pls is working fine :

Oracle Applications DBA Field Guide

http://hostname.domainname:port/pls/$SID so if you installed vision instance with SID as VIS11I your SID here is VIS11II this sometime in documents also called as TWO_TASK. You should see output from procedure FND_WEB.PING . If not check that -
A) database listener is Up
B) GUEST User is not end dated & password is correct.
C) dbc (database connect descriptor) file is corerct at $FND_TOP/secure
D) apps password is correct in wdbsvr.app at $IAS_ORACLE_HOME/Apache/modplsql/cfg

Login to Application :

Oracle Applications DBA Field Guide

Login to application with Application User to confirm login is working fine , if not check mod_pls for any issues.

Check Form Server is working :

Oracle Applications DBA Field Guide

Click on any Core Responsibility like "System Administrator", If you are facing any problem opening form Applet
A) Check jinitiator is installed, if not do you have access to install jinitiator
B) Try clearing cache from jinitiator
C) Check forms server parameters are configured properly in appsweb_$CONTEXT_NAME.cfg
D) Check if form server listener is Up : netstat -an | grep form_server_port

Check Concurrent Manager is Up & Running :

Oracle Applications DBA Field Guide

Select "Administer Concurrent Manager" & check if "Actual" & "Target" are same.

Check Reports can display properly :

Oracle Applications DBA Field Guide

Change "Active Users" reports output from "Text file" to "PDF" from Define Concurrent Request Screen. Submit Active Users request & click on Output , check if you can se report in PDF format.

Check Apps Listener is Up :

Oracle Applications DBA Field Guide

Apps listener is different from database listener, Apps Listener is used for various purpose one is to check output & log files in concurrent requests. Check if apps listener is fine by clicking on log file & output file for Active Users request you submitted in Step 7 on previous page. If you encounter any issues while trying to access Log & Output file issue might be with Oracle Apps Listener. Check if adalnctl.sh (where ad is apps dba, aln is apps listener and ctl is control) on application tier started successfully. If yes then check this query (select logfile_name, logfile_node_name, outfile_name, outfile_node_name from fnd_concurrent_requests where request_id=[your request id number].

Check if Workflow is Up :

Oracle Applications DBA Field Guide

Login to OAM (Oracle Application Manager) using url mentioned in step 2 in previous page. After login, On top right of page from "Nevigate to" select "Workflow Manager" from drop down menu and click on GO button. Check "Notification Mailers" is Up .

Check if Discoverer 4i is Up : There are two type of discoverer 4i
Discoverer Viewer - Check http://yourhostname:port/discoverer4i/viewer
Discoverer Plus Check http://yourhostname:port/discwb4/html/english/welcome.htm