By "no responding" do you mean that you can't connect to it in any way? Or do you mean that some queries won't return? Or do you mean that some users are reporting it as blocked? Remember, we're not sitting in your chair, so being as clear as possible with the question will make it more likely to get an answer that's useful to you. If you can connect to SQL Server, use sys.dm_exec_requests to understand what is currently running on the machine and how much resources are being used and if there are blocked processes.