Did you upgrade your Desktop to 9.1? It is recommended that both Server and Desktop be the same release number.
Can you give us a screenshot on the issue 1.
"then i provide credentials but it's not connecting to server.still it's showing credentials page."
I would suggest creating a support ticket with our Technical support department. There are a number of potential issues that might be causing this issue, and we are best set up in support to help identify these!
A few things that we will want to know-
1) A screenshot! (Monisha Yartha is a smart cookie for asking for this!)
2) When you say you are using SSO- Are you using Active Directory? Kerberos?
3) A copy of your Tableau Desktop logs that show when you try to log on. (instructions here: http://kb.tableau.com/articles/knowledgebase/sending-tableau-desktop-log-files)
4) What happens if you try to sign on to the Tableau Server using a browser window? can you still connect directly to the server?
Our Triage department will be happy to help you identify why you can't log in, starting with the information above!