After lock the iPad mini normally and so my stuff. Came back to use iPad to check something online. However, the device won't wake up no matter what. Press sleep/weak button did not help nor press home button. The device will wake up unless I do hard rest, which is home + sleep for few second. This happens to my iPhone 4S as well. There is no crash report or the crash report is empty, so I cannot trace what really happened back then.