Srikanth ,
initially , I think you should try to change the Fiori Login screen Theme at System Logon Configuration.
Please have a look at this thread to achieve it .
How to change the Fiori logon screen
Once the Logon screen is set as required (traditional flower screen) . please check your single signon configuration,
Also do you find any errors as in the below screen when accessing the Fiori Logon screen in desktop?
Regards
Virinchy