Uninstall Oracle from Server Completely

Uninstall Oracle

# Stop any Oracle services that have been left running.
Start->Settings->Control Panel->Services
Look for any services with names starting with ‘Oracle’ and stop them.
* Uninstall all Oracle components using the Oracle Universal Installer (OUI).
* Run regedit.exe and delete the HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE key. This contains registry entires for all Oracle products.
* Delete any references to Oracle services left behind in the following part of the registry:
HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Ora*
It should be pretty obvious which ones relate to Oracle.
* Reboot your machine.
* Delete the "C:\Oracle" directory, or whatever directory is your ORACLE_BASE.
* Delete the "C:\Program Files\Oracle" directory.
* Delete the C:\Documents and Settings\All Users\Start Menu\Programs\Oracle*
* Empty the contents of your "c:\temp" directory.
* Empty your recycle bin.

# Delete the Oracle Start Menu shortcuts directory:
Start->Settings->Control Panel->System->Advanced->Environment Variables
Edit both of the environment variables user PATH and system PATH. Remove any Oracle references in them.
# Remove Oracle refereces from the path. To edit your path go to:
# Remove Oracle.DataAccess and any Polic.Oracle files from the GAC which is at:
C:\Windows\assembly\