I have old bank accounts showing in my dashboard, they have transactions in that aren't reconciled and show a negative balance, where do I start with this please?

Hello Ladywood40-live-c, Thanks for posting on the community page, 

In QuickBooks balance is the total of bank transactions recorded under the bank account in chart of accounts.

Reasons why In QB balance is different from the bank balance:

1 . Missing transactions that need to be recorded

2. Duplicate transactions

3. No opening balance created for the bank account

Last option is bank reconciliation

To fix the difference you need to get a copy of your bank statement and compare it with the recorded transactions in the bank account inside QuickBooks to reconcile.