intermittent connection issue - connecting with windows authentication

Hi,
I need thoughts and help on the following
Users facing intermittent authentication issues - using windows credentials. When i checked the database it is up and running and even the server on which it is hosted. The point is that when i tried to connect to the server from querly analyzer it doesnt even allowed me to connect but the sql authentication was succesfull. I m stuck and dont see any way ahead.
I found few things when i googled for the above case - Windows AD Token / Memory Issue.