why does my mail application open when i turn the computer on and how do i stop it?

Open Accounts preferences and click on Login Items tab. If you see Mail listed there, then select it and click on the Delete [-] button.

If that isn't correct, then look in the /Library/StartupItems/ and/or /Home/Library/StartupItems/ folder for anything that is launching Mail such as an add-on you've downloaded, then delete it.

If your on 10.5.6 (or the lastLeopard version 10.5.8) as your ASC profile indicates...?

Then go to: Apple > System Preferences > Accounts . Login Items and remove Mail from the list of item set to open at ligin.

If your running a newer 10.6, 10.7 or 10.8 OS X version, please update your ASC profile so that we can assist you with those.