This has only happened when I try to edit pictures in Lightroom. I have never had problems before, just editing in Photoshop cs6. These pictures have been shot on a Nikon D5200 as raw files (.nef).
Another weird thing is when I view them in the window explorer, they look fine. Then a second later they are all screwed up.
Caused by a hardware problem, most like. Lr is pretty resource intensive and stresses hardware more than most other software; so this might be a dodgy RAM stick, a failing hard drive (I've had that one), a faulty memory card...
Do a site search for "image corruption".
Your second and third screen caps are of Picasa, not the MS viewer, which is initially showing the jpg embedded by the camera in the NEF and only afterwards trying to create a display from the corrupted Raw data. It not infrequently happens that when the Raw is corrupted the jpg remains ok. If the image is important, you can salvage something with Instant JPEG from Raw
Card reader failure could also be the problem.