Computer not turning on/will only turn on when plugged in

[annabelle27]

For a while now my laptop has not been turning on unless its plugged in and charging, obviously this is not ideal as i want to be able to take my laptop places such as lectures but cant as it wont turn on without being plugged in. THis hasnt always been the case and only started a few motnhs ago. Even more annoying than this is that sometimes it wont even turn, plugged in or not. I followed HP instructions for how to fix this and eventually get it to turn back on, but then it carries on not working without being plugged in then mabye a ouple days or a week later wont turn on at all (even when plugged in). So it kind of just follows this cycle and i dont know what to do to fix it and its really frustrating. Also its not got anything to do with the charge as by the time i get it on the battery is usually quite full so im really unsure of the problem. Please Help.  

[ieee488]

Run HP diagnostics at bootup.