Customers of HSBC were left unable to use cash machines and online banking following an outage in the bank's mainframe computer.
This is the second IT failure in about six months and comes at a time the bank is upgrading its entire business infrastructure.
An HSBC spokesman said the network is back up after the bank identified the cause as a "mainframe outage." He said the bank will investigate further.
HSBC is going through major upgrades as it integrates its entire business onto a common platform known as One HSBC.
HSBC launched investigation after systems failed in June leaving customers unable to withdraw cash from ATMs and without online banking.
In February 2008, an upgrade to a telephone banking system for business customers caused some HSBC customers problems.
HSBC said at the time that some customers could not complete some debit transactions. "The issue was caused when new coding was put into the telephone banking service for business customers."