Computer shuts down

[ded2day]

Hey. I have recently acquired a problem when I leave my computer on, it will shutdown in about 15 minutes when the screensaver comes on. It will also boot up again, but it says there is a boot disk error, and it won't find my hard drive until I swap the sata port. I thought it was a heat issue, I do have fans to cool it. I thought it might be my graphics card, so I purchased a new one (which I wanted to do), I even changed my power supply to a bigger wattage. I am tempted of getting a motherboard which I don't want to do it's my last resort. Is it a virus or malware?