HELP!! Short Sale (Re)Negotiation After Bank Approval??

[Barbara Sheppard]

For a short sale property, can the buyer renegotiate the price with the bank AFTER the bank/lender has already accepted the offer?  

Situation

The property was clearly in very bad shape to begin with. Several offers were rejected until we came up to the bank's asking price (their property valuation).  Our further visual inspections after offer acceptance revealed repair costs that are significantly higher than initially anticipated when the offer was submitted.  Closing is scheduled to take place in a few days!  This has been a lengthy process and while the goal is to close on the property, we cannot do it at the price that has been accepted by the bank.  

Please advise, what can/should we do?  Can we go directly to the bank to renegotiate?   Do we walk away, and if so, what consequences will there be? 

Thank you in advance for your help.