Stuck at Windows loading screen?

[Mopreme]

Ladies & Gentlemen,
I have been trying to get this notebook Acer S3 to run properly for a few days now and I think I am going to need some help to get anywhere.
The issue started like this:

I turned the PC off after a normal day using Word etc. I turn it on, and it just stayed at the Windows logo (loading). Nothing happened and I couldn't get it booting even from the startup-repair thing. So, I did a clean install (talking Win8.1 here), everything was now great! Next day as I have everything on it again, I take it with me to school, after an hour or two of use, same story, stuck at Windows logo. I figured it was the HDD that was the issue, so I replaced that with another, did a clean install of Win8.1 again, and boom, after nothing but few hours this time it goes to the same story with that loading screen.
Any clues? Would love to know what is causing this if it isn't the HDD? I am completely lost after this 2nd clean install of Windows.
Any help is much appreciated! Please; ideas

[Janar]

Do a RAM test. I have used memtest86+ myself.