If you want to remove oracle manually. follow the following simple steps.
1. Remove oracle from Registry.
2. Remove oracle installed folder.
3. Remove oracle from folder from program file or program files (x86)
4. Remove oracle services.
Ø Press Windows key + R
Open the Dialog box show all the services
Then show oracle services
This services you are find specific secvices after choose a remove services name
Press windows key and search regedit.exe
Press windows key + R and type regedit.exe
Ø Remove oracle key from HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services.
Delete each oracle key independently.
Ø Remove folder where oracle is installed. Oracle 10g generally installed with the name oracle.
Ø Remove oracle folder from program files or program files (x86).
8. Now you have manually uninstalled Oracle 10g from your PC.
Ø Restart your PC.
Ø Then reinstall oracle data base. software