Black screen, blinking underscore top left corner

Hello I'm AJ & I need help. . . badly :/
so about 5 months ago my PC was just fine, but it started crashing randomly,I would have to restart it manualy using the power button,now the computer won't even boot. Everytime I turn it on the computer just stays on a black blank screen with a blinking underscore or cursor at the topleft corner.
?? ): how can I fix this . . . if you need more details on anything, please just comment.
 
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