Why is database hanging?
If you can't get a session started to be able to look at V$ tables etc., I'm afraid that you'll be out of luck. Sometimes Statspack can capture some information if you have it implemented to snapshot periodically. If you're having a fairly routine occurrence of "hang-ups", I'd recommend you put something in place to monitor your database and alert you to conditions approaching threshold values that may signal a problem. You can write your own procedures to do this or you can use OEM to send you alerts or buy a third-party tool (Quest software has several for instance) that will assist you.