So, I have a PC I got from a friend, and it was working when he had it. Now, when I turn it on, it takes me to the Computer startup screen, and I have to press F1 to start up Windows. So I do that, and when it gets to the Windows Startup Screen, it shuts off. Then, when I turn it one, it tells me that it shut off due to a thermal event (I know this means that it overheated), however, the heatsink is connected properly, and all of the fans are working. I have just applied new thermal paste after cleaning the old paste off, but it still doesn't work. What do I do?