Hi kefa
The accounts that are listed in the Bank transactions window would be the bank (or credit card) accounts that you have imported at the statement for using the Import Statement OR have received bank feeds on. For an account not to be listed it means that you haven't received bank feeds on it or imported a statement. In saying that, transactions for that account should still be listed in the Banking>>Find transactions window.
Please note: I assumed by Cash transactions you have meant transactions through a "cash" bank account within your MYOB Essentials product. Cash transactions in accounting can also mean payment basis - which should be occurring when you make payment on your transactions (as opposed to accrual which is when you invoice).