There're a couple of reasons why your QuickBooks beginning balance isn't the same with your bank statement. This includes outstanding or uncleared transactions, duplicate transactions, and modified or deleted transactions.
Re: QB beginning balance doesn't match bank statement
I have used Quickbooks for 20 years and have always reconciled my bank statement to quickbooks until a virus attached to my Quickbooks four months ago. Mac hard drive was cleaned and QB has not worked correctly since then. Changed for days ago from QB Desktop to QB online.
Bank statement on December 29, 2017 and QB do not match. Need to correct this problem before reconciling year 2018 bank statements.
There are multiple reasons why a bank balance may not match the register in QuickBooks Online (QBO). One example of this could be an outstanding transaction, such as a check that hasn't cleared the financial institution. In an instance like that, it's generally recommended to wait for it to clear from your financial institution. Naturally, there can be a delay with transactions reaching For Review, due to a person waiting to deposit it and processing times at the bank.
Another reason is deleted or duplicate transactions. Since QuickBooks shows a negative balance, I would recommend looking first for duplicate transactions.