Resetting Checking Account Caused Huge Difference Between Online Balance and Ending Balance

Had to reset my checking account because my bank has us change passwords every-now-and-then. I had to reset because I went into Password Vault to change my password but it wasn't required?
I reset my account and linking it to my existing.
But, now Quicken shows that I ending balance is -$800 and the online balance is $300.
I over drew by $800.00???

Any idea why this happened???
James