National Australia Bank scrambled its tech team on Friday to fix a computer system failure that brought down its ATM, Eftpos, internet and phone banking networks.The crash, which impacted on the NAB's core banking mainframes, also stalled the HiCAPS network used for medical billing, which was out of action for several hours.The bank began progressively bringing its systems online by early afternoon. However, NAB customers whose transactions failed during the period the computer systems were down had to wait until Saturday morning before their account details were brought up to date.The bank said it recognised and regretted the inconvenience to customers.Earlier in the week, it was St George customers who were inconvenienced when the bank's website was offline for several hours. For most of the day, customers accessing the website were greeted with a sign saying that the bank was experiencing "technical difficulties" with its website.The bank's core systems, however, weren't impacted and customers were still able to access online banking via a still active window on the otherwise stalled website.