My 9810 has started turning off by itself shortly after turning on. Had it for less than a month!

I have it set to run on at a certain time each morning which I hear it do but, if I don't make any selections on the phone, it turns itself off. At first I thought it was the holster but, I've tried laying it on the counter while making coffee & it still turned off. It seems that if I open anything, like open my calendar for the day, it will remain on after that.

Is there a setting that I'm missing that may cause it to shut down due to inactivity? Any other ideas?

Thx in advance for any ideas.