A similar thing happened to me some time ago...
I switched on my computer and noticed that my Hard Drive light was constantly lit, for ages and ages...

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I looked in my various Folders and they were gradually being emptied, one by one...

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I switched off the Computer quickly...but too late...there was nothing left..

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I ended up with a Hard Drive full of empty, yellow Folders!
I think a Virus scan revealed a Virus, Trojan, or some other infection had crept in, via the 'Net....

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I think I finished up purchasing another Hard Drive, and re-installing everything again...

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That was a bad Day!
Paul...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.