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If you were not logged in to your AOL account at the time (or even better, if your computer had been turned Off) then that would not have been possible. Just a word to the wise for next time.
If AOL mail was deleted, contact AOL immediately, not later, and see if they can restore the contents of your account. This is something that only AOL can do for you in such a case (unless you had a (fairly recent, complete) backup of your Personal Folders or Personal Mailbox - or whatever the most recent version of AOL now calls it... in which case that would be where to go to restore your email accounts contents...) and they may not be able to do so if you do not act fairly rapidly.