My sister was using her HP 15-ac121dx she closed it and set aside for a few when she opened it back up it was just a blank screen. I took out the battery unplugged it and all of that and nothing helped. Basically if you press the power the screen turns on, but it's just blank and it just stays there if i press any of the 'f' keys to try to get a bios feature like boot order or something it just freezes. example press f9 and in the bottom left corner it says 'f9...change boot device order' but that's it just stays there i then have to unplug it and try another key and it does the same thing.
Shortly after I started working on it i noticed that when i first press the power button there is a clicking sound coming from the bottom right side of the laptop after opening it as suspected this is where the hard drive is. If it were a drive failure wouldn't i still be able to use the 'f' key features like system restore rather than it just freezing on that screen.
Just to check i took the memory chips out and put them back in and checked the connection of the hard drive i also took out the cmos battery for 5 min. After resetting the cmos i got a message when i first turned it on that the computer had to be restarted again by pressing enter. After doing this it returned to doing what it was doing before.

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