10.8 ... why goes macbook into deep hybernation?

My macbook [unibody, core2duo, late 2008,hdd no ssd 13'', new battery since 3 weeks] wakes up after I close des cover e.g. twice in 30 min. After that - without no scheme to detect - it goes into deep hibernation or something else. I have to push start button to have it ready to work again after 1 min. This is unbelievable - complete change of working with it. Why? Will change brand if that is not corrected ........ AArghh! WLAN is lost in the meantime what should not be in powerr nap state