Device keeps going to sleep

I've had my Garmin 530 for 2 years though I haven't ridden as much as usual. Recently when I start the timer at the beginning of a ride, within about 20 seconds I get the message "going to sleep in 3, 2, 1" and it goes to sleep. It's still recording data but I need to be able to keep my screen on so I can see average speed, etc. (I lead rides for a bike club) I have tried to trouble shoot this but can't seem to find an answer. I wondered if I went back to default settings? Any ideas?