Just posting an update on this. Surprisingly db2diag.log reached 175GB on this server. So i am unable to open it directly or using any of the options of db2diag command like time/archive etc. Its throwing, some other process has lock on this file so unable to open it. I am thinking that this huge db2diag.log file caused the hang of DB2. We are trying to delete this file. Hoping this resolves the problem on this Windows server. If not, i should be able to open the new db2diag.log file generated after deleting the old file to troubleshoot the problem.