Unstalling all Oracle products from Windows systems

•  Using the Oracle Universal Installer (OUI) to Uninstall all Oracle components:

• cmd> regedit.exe and delete the HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE key.

• Delete all references to Oracle services  following part of the registry (HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/Ora*).

• Reboot your machine.

• Delete the "your ORACLE_BASE." directory 

• Delete the "C:\Program Files\Oracle" directory.

• Empty   your recycle bin.