A few months ago, my pc was running perfectly until my sisters boyfriend suggested that I clean it because it was getting dusty. We took the whole thing apart, cleaned it, and put everything back together. Now, when I turn it on, it goes to the screen that has the boot menu and BIOS options. After that screen, it goes to this black screen with a blinking underscore at the top left corner and stays there. It doesn't get past that screen. If I try to go to boot menu, safe mode, or BIOS settings, it freezes the screen and doesn't even get to the screen with the underscore. I've even tried putting in another HDD but I get the same problem. Help?