Problem with electronic watering system

I bought one of these things last year:

https://www.tooltime.co.uk/shoppingcart/products/Automatic-Electronic-Garden-Water-Timer-With-Lcd-Digital-Display.html

I've just got it ready to use while on holiday and it seems to be faulty. I can set the day and time OK but pressing On/Off or Program does nothing.

Does anyone who has one of these have any suggestions? I can't see a reset button anywhere and the manual doesn't help.

Thanks.

Thanks. I'm using rechargeables, which I charged up fully last night. (The same batteries worked OK last year for many weeks).

I'll try to find some standard batteries to try. You never know.