Mother Board is (DG41RQ), Processor (2.93 GHZ) , RAM (4 GB) , My External Hard Drive is Samsung (1.5 TB)..When i unplugged (Safely Remove) my system got Hanged . I am using Ubuntu 11.10 DVD version
This is a known bug that has been fixed in a kernel upgrade. The upgrade has not yet been released though likely will be in the next couple of weeks or so. (currently in oneiric-proposed for testing of the 'whole' of the upgrade, not just this one issue.
bug specific to this issue https://bugs.launchpad.net/ubuntu/+source/linux/+bug/844957