Detailed explanation on how to report bugs can be found here:
https://help.ubuntu.com/community/ReportingBugs
But since you are a new user, its best you check here on the forum first so you dont report bugs which arent bugs. Your problem with the failing disk message is a known bug, I dont think its useful to report it again. The issue with not shutting down I would report as in the bug report I linked I dont see anyone using Karmic (9.10).
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