k5 "freezes"

taking a few shots today using k5 and 100mm macro wr (indoors), the camera would quite often freeze up. if i turned it off, then back on again it would be ok for a few shots then do it again. It would tend to do it more after i had left it for a few minutes, say to rearrange the subject.
there would be no autofocus noise....nothing.
it had a near fully charged battery, and i use back button focus if thats any help.
any ideas?

Possibly dirty electrical connectors.........are you getting any error code such as the: F-- ?

Do you have the Auto Power Off set to something like 5 minutes? I've set mine to 30 minutes to avoid the camera switching itself off too soon.

Thanks dingo for the reply, but i think john has got it!
i bought a second k5 body from a forum member and thought i had set it up the same as the first......except the auto power off, it was set to 1 minute.
i did think though, that when it went into auto power off, a press on any button would wake the camera?

Chers,
simon.