Canon Powershot A720 IS will not power on

A720 is16 months old and was working perfectly apart from date/time memory loss because date battery replacement needed. New 1220 battery purchased & fitted, but subsequently unable to power camera up; completely dead, no clicks or rattles. Refitted old 1220 battery, expecting to see date reminder on power up, but camera still dead. Refitted new 1220 plus new lithium AAs several times (all with correct polarity), plus different SD memory card, all to no avail. Camera in very good condition, but cleaned contacts anyway. Zero signs of life.

Canon's own support knowledgebase no help and likely minimum $100 for someone to open camera up. Any ideas?
Mike.