* 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:
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.
* Empty the contents of your "C:\temp" directory.
* Empty your recycle bin.