Siebel Server is not coming up...What should we check?

1. Validate that the .srf file is not corrupt by testing the srf on a dedicated environment.
if the dedicated client is facing issues possibly 2 reasons must be there
a.srf file is corrupt
b.db itself is down
Take the necessary action

2. Stop siebel servers after executing ./siebenv.sh and command stop_server all

3. Check that no Siebel processes for the enterprise are still running.
Windows: Check Task Manager for any Siebel process for the enterprise still running.
Solaris: Execute ps -ef | grep [directory path] (eg. ps -ef | grep /app/siebel/siebsrvr).
ps -ef|grep sieb also finds all active siebel process
Ensure that all processes for that enterprise are killed.
use kill -9 pid to achieve the same

4. Delete any file that exists in directory %SIEBEL_ROOT%\sys with name like:
osdf.[SiebelEnterprise].[SiebelServer]
Where
[SiebelEnterprise] = The Siebel Enterprise name
[SiebelServer] = The Siebel Server name.

5. Delete any file that exists in directory %SIEBEL_ROOT%\admin with name like:
*.shm
dhm files are shared memory files. This file should be automatically deleted when the Siebel server is shut down, if it still exists when the Siebel server is down then it has been corrupted and not correctly removed.

6.Delete fdr and core files as these file eat up large amounts of memory.

7.Cleanup unwanted logarchive and log files so that fresh logs can be monitered and space can be freed up.

8.Try to restart server after executing ./siebenv.sh and command start_server all
Note- At this point if the server still does not restart, you need to check the enterprise log for the reason. The enterprise log is located in:
%SIEBEL_ROOT%\enterprises\[SiebelEnterprise]\[SiebelServer]\log
The enterprise log has name with format:
[SiebelEnterprise].[SiebelServer].log

9. If no enterprise logs are getting creted there are connectivity issues with the database:
i.e change of db password for SADMIN user
db server is down
(Come to this conclusion ony if you skipped the first step)
run odbcsql from siebsrvr/bin to check connectivity issues
odbcsql /u SADMIN /p SADMIN /s DSN Name

10. Any changes which lead to the corruption of siebns.dat will also result in the servers not coming up.
usually NameSrvr logs tell us connectivity related information and errors like key not found.Try reverting to an old working siebns.dat file.

11.If the environment is LDAP authenticated any changes in the LDAP trees can also affect the environment.please verify the same.

12.Check the SCBroker and SRBroker logs;you would get a hint.

13.Use netstat -an|grep 2320 for verifying that the gateway service port is listening.

14.Use netstat -an|grep 2321 for verifing that the SRBroker/SCBroker port is listening
So that is a long list.Thought there can be other reasons too; I have only mentioned those encountered by me.I will keep on updating when I find newer reasons.Till then stay tuned.