One of my friend was installing cluster SQL Server, installation was stopped in the middle of something and he was not able to remove the SQL Server from add/remove programs or SQL Server setup. He has deleted the registry, folder manually but still he can see the SQL Server Services in Services.msc. He called me for the issue, I have provided him the below solution and it will work.
1) Go to command prompt and use SC command to delete service
sc delete sqlserveragent
sc delete mssqlserver
2) You have to also delete the services registry entry using regedit