u must first go to universal installer in oracle installtion in program files,and then
deinsall all product ,then open services in control panel and stop all services
belong to oracle ,and then go to regedit and remove all files in your machine
belong to oracle installation and then delete the all oracle`s files in your hard
then boot your machin,and i advise you to boot your machin in each step you do
,if there is any problem post to me