Digital clocks on cookers typically run indirectly from the mains - they don't have a battery - you do not say the make or model of your cooker.
Often when the power is interrupted and comes back on the clock flashes until it's given a time - any time will do - on my cooker I hold down the two leftmost buttons and use plus and minus to set the clock - then it all works again.
Your cooker may be different
Good luck...
Gordon of Khartoum, September 2014
