I'm kind of new here, so didn't konw where to post this!!

I have a asus pro 55S Series with running Ubuntu 10.04 LTS,
I got a few probleem with my ubuntu,

First I got by my computer janitor a error, when I start it up then it shows me this message

Essential package dash is missing. There may be problems with apt sources.list or Packages files may be missing?

after that it colse it slef!! How can I fix this?

The next error is that my update manager show the next error if i try to find new updates

Could not download all repository indexes

The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct.

And also does my update manager nothing? It's stress me out!!

And the next error is that when I try to upgrade my ubuntu to 10.10 then it wil close it self ather hi is done with perpeing the upgrades, what schould I do about it ?

I need some help