Manually uninstalling the Oracle from WinOS platform .

I had to do it for the Documentum installation and it sucks to do all these steps if you really mesh up the oracle installation. I did this to try some latest Documentum product testing and i noted down these steps if i need them in future or these can be of any help to anybody.No guarantee for any damage to system because these steps involve registry modifications and can really cause harm to your server if you try them on production environments(BE AWARE ). It was all hit and trial to re-install the oracle as oracle un-installer doesn't clean-up the system if you need to reinstall and it will be nightmare unless you really clean up the previous installations of oracle from the system.

A. Removing Components on Windows OS.
To remove all Oracle components from a computer on Windows OS:

1. Check privileges:
1.a. Ensure you are logged in as a user with Administrator privileges.

2. Stop all Oracle services (if any are running):
2.a. Right click My Computer > Manage > Services and Applications > Services

2.b. If any Oracle services (their names begin with Oracle) exist and have
the status Started, select the service and click Stop.

2.c. Click Close to exit the Services window.

2.d. Close the Control Panel/Computer Management window.

3. Remove the entries in the Windows registry:
3.a. Start the registry editor:
Choose Start > Run > regedt32

3.b. Go to HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE
Note the value of the key INST_LOC, this is the location of the Oracle Universal
Installer. The default location is Installation Drive(C:or D:):\Program Files\Oracle\Inventory. If this value is different, make note of it, so we can delete these files later.
Delete this ORACLE key.

3.c. Go to HKEY_LOCAL_MACHINE\SOFTWARE\ODBC and expand all subkeys and
remove all keys under here which are related with the
"Oracle ODBC Driver"

3.d. Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services and remove
all keys under here that begin with ORACLE or ORAWEB.

3.e. Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EventLog\...
\Application and remove all keys under here that begin with ORACLE.

3.f. Go to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall
and remove any entries related to Oracle.

3.g. Go to HKEY_CLASSES_ROOT, remove all keys that begin with Oracle, OraPerf or
OraOLEDB

3.h. Close the registry.

4. Clean up the environment settings:
4.a. NT: Choose Start > Settings > Control Panel > System > Environment tab
2000: Choose Start > Settings > Control Panel > System > Advanced tab >
Environment variables.

4.b. At "System Variables" click on the variable PATH in order to modify
the value. For example, you may see a path similar to this one:
C:\ORACLE\ORA81\BIN;C:\PROGRAM FILES\ORACLE\JRE\1.1.7\BIN

4.c. If an %ORACLE_HOME% was installed, remove this %ORACLE_HOME%\BIN path.

4.d. If JRE was installed by Oracle, remove the JRE path.

4.e. If there is a CLASSPATH variable under "System Variables", first make note
of the path defined, then delete it. This variable can be added back at
a later date if needed.

4.f. Check if there are any other Oracle variables set in "System Variables",
ORACLE_HOME, ORACLE_SID or TNS_ADMIN. If these exist, delete them also.

4.g. Click on APPLY and OK.

4.h. Close the Control Panel window.

5. Delete the software and icons:
5.a.Choose Start > Programs > Accessories > Windows NT Explorer.

5.b. Go to SYSTEM_DRIVE:\WINNT\PROFILES\ALL USERS\START MENU\PROGRAMS
OR Go to SYSTEM_DRIVE:\DOCUMENTS AND SETTINGS\ALL USERS\START MENU\PROGRAMS


and delete the following icons:
- Oracle - HOME_NAME
where HOME_NAME is the previous Oracle home name.
- Oracle Installation Products

5.c. Go to SYSTEM_DRIVE:\Program Files\Oracle or the location of INST_LOC as
noted earlier in step 3.b and delete this directory.

5.d Go to SYSTEM_DRIVE:\Temp and delete all files and directories in here.

5.e. Go to the drive where the Oracle software is installed on your machine
and delete all ORACLE_BASE directories on your hard drive.

5.f. Close the Windows Explorer.

6. Finish the removal

7 Reboot your computer.