Laptop Black

Why does my laptop screen black out?
Colored lines suddenly appear on my laptop screen, at this time my mouse is still able to be moved, then after a while it hangs, the mouse cannot move anymore. The screen turns black, and if music was playing, it will still play when the screen is black.
This has happened four times. After if happened i did a virus scan and nothing came up. Sometimes these lines just flash on my screen a while and is gone, but sometimes that black screen happens. Why?
Please help thanks.
Maybe something is wrong with your laptop.
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