It has to be said:
"DETCORD!"
Not too far off, perhaps. I had two Dell Dimension 4100s (one mine, the other my wife's). Mine got hosed by some kind of virus that acted a bit like that. I was using hers while working on mine, and then HERS got hosed. I ultimately reformatted both hard drives and reinstalled the apps we needed, then restored what data I had been able to recover from both drives by installing each as a slave drive in a third machine of similar vintage. (And my wife wonders why I keep spares.)
I hate viruses. The people who create them are beneath contempt.